feat(download): M94 下载页换成真组件 + 真快照 + 真指令（PAGEDL）

页面（crates/app-iced/src/pages/download*）：
- Tabs（分类）/ ListItem（版本行）/ filled 安装按钮 / progress / EmptyState / divider
  全部取自 components/ 的真组件；页头动作换成 buttons::text
- 数据只吃 pages::download::Download（app/view.rs 由 AppState 快照转，installed_only 与
  download_query 照用）；页面自己不留业务状态，交互只发意图
- 状态：加载（不确定进度 + 文案）/ 空（EmptyState + 刷新 CTA）/ 有数据 / 安装中 / 安装失败
  （失败给可读文案 + 「打开日志」出口）

接线（追加式）：
- pages::Message 加 SelectVersion / InstallVersion / CancelInstall / SetCategory
- app/update.rs 翻成 AppCommand::{InstallVersion, CancelInstall, ListVersions}
  （SelectVersion 只改视图模型；「刷新」= 当前分类重新拉，全部走 RefreshAll）
- pages::Model 加 download 字段

文案：28 个 Download* key 进中英两套 catalog（一行一个 key 的全语言）；页面零中文字面量，
  core 的中文阶段串（InstallStage::label / message）一律不进界面

i18n 结构：catalog.rs 的既有测试模块原样外置到 catalog/tests.rs（392 行 → 282 行，
  逐字未改），新 key 才装得下 400 行硬上限

测试：app-iced 276 + i18n 23 全绿；clippy -D warnings 与 fmt --check 干净

crates/i18n/src/catalog.rs

@@ -115,6 +115,55 @@ catalog! {
 
     // ── core / presenter 只给了中文串、UI 又不许画原文时的兜底（见 `bridge`）
     CoreTextUntranslated => ("[system text not translated]", "［未翻译的系统文案］"),
+
+    // --- download page (M94) ---
+    // 下载页（`crates/app-iced/src/pages/download`）。一句话一个 key：带变量的句子用 `{name}`，
+    // 页面只做 `Catalog::render`，不拼片段（`bridge` 的规矩 1）。
+    DownloadTitle => ("Downloads", "下载"),
+    DownloadSubtitle => ("Version list from the official manifest", "来自官方版本清单的版本列表"),
+    DownloadRefresh => ("Refresh", "刷新"),
+    DownloadInstall => ("Install", "安装"),
+    DownloadCancel => ("Cancel install", "取消安装"),
+    DownloadInstalled => ("Installed", "已安装"),
+    DownloadCount => ("{count} versions", "{count} 个版本"),
+    DownloadRowSupporting => ("{kind} · released {date}", "{kind} · 发布于 {date}"),
+    DownloadSelectHint => ("Pick a version, then install", "选一个版本再安装"),
+    DownloadSelected => ("Selected {version}", "已选 {version}"),
+    DownloadLoading => ("Loading the version list…", "正在加载版本列表…"),
+    DownloadLoadingHint => (
+        "The list appears after the first successful fetch; this page never goes blank.",
+        "首次拉取成功后这里会出现版本列表；这一页不会是一片白。"
+    ),
+    DownloadEmptyTitle => ("No matching versions", "没有匹配的版本"),
+    DownloadEmptyBody => (
+        "Switch the category or clear the filter to see more.",
+        "换一个分类或清掉筛选后再看。"
+    ),
+    DownloadCategoryAll => ("All", "全部"),
+    DownloadCategoryRelease => ("Release", "正式版"),
+    DownloadCategorySnapshot => ("Snapshot", "预览版"),
+    DownloadCategoryAncient => ("Ancient", "远古版"),
+    DownloadStagePlanning => ("Planning", "解析版本"),
+    DownloadStageDownloading => ("Downloading files", "下载文件"),
+    DownloadStageInstalling => ("Building the version", "生成版本"),
+    DownloadStageRegistering => ("Registering the instance", "登记实例"),
+    DownloadStageDone => ("Done", "已完成"),
+    DownloadStageFailed => ("Install failed", "安装失败"),
+    DownloadStageCancelled => ("Install cancelled", "安装已取消"),
+    DownloadProgress => (
+        "{done}/{total} files",
+        "{done}/{total} 文件"
+    ),
+    DownloadProgressUnknown => ("Waiting for the first file…", "等第一个文件…"),
+    // 速率与剩余时间是两个独立短语，各占一个 key（`DownloadRate` 只负责把它们排成一行）
+    DownloadRate => ("{speed} · {eta}", "{speed}，{eta}"),
+    DownloadEtaSecs => ("{secs}s left", "剩 {secs}s"),
+    DownloadEtaMins => ("{mins}m{secs}s left", "剩 {mins}m{secs}s"),
+    DownloadFailedHint => (
+        "The Logs page has the full reason.",
+        "完整原因在日志页。"
+    ),
+    DownloadOpenLogs => ("Open logs", "打开日志"),
 }
 
 /// 一套语言的目录（不可变；`Copy`，随手传值）。
@@ -229,164 +278,5 @@ pub fn placeholders(text: &str) -> Vec<&str> {
     }
     found
 }
-
 #[cfg(test)]
-mod tests {
-    use super::*;
-
-    /// 手写一套**故意缺条**的目录（不经过 `catalog!`，模拟后续 mission 的注入表）。
-    const PARTIAL_ZH: &[(Key, &str)] = &[
-        (Key::NavInstances, "实例"),
-        (Key::NavLogs, "日志"),
-        (Key::NavSettings, "设置"),
-        (Key::NavDownload, "下载"),
-        (Key::InstancesNew, "新建实例"),
-        (Key::InstancesImport, "导入"),
-        (Key::InstancesBack, "返回实例列表"),
-        (Key::InstancesPlay, "启动"),
-        (Key::InstancesLastPlayed, "上次游玩 {when}"),
-        (Key::InstancesEmptyTitle, "未选择实例"),
-        (Key::InstancesEmptyBody, "选择一个实例查看详情。"),
-        (Key::LoaderVanilla, "原版"),
-        (Key::LaunchOutcomeNormal, "正常结束"),
-        (Key::LaunchOutcomeCrash, "游戏崩溃"),
-        // 缺：LaunchOutcomeSilent / LaunchFailedWithCode / FontCjk* / Settings* / CoreTextUntranslated
-    ];
-
-    #[test]
-    fn built_in_catalogs_have_every_key() {
-        // 抓得住：`catalog!` 的成对生成被绕开（有人改回「两套各写一遍」并漏了一条 / 抄重了一条）。
-        //         判据是**集合相等**：`Key` 枚举拦住了「表里有、枚举没有」，这里拦反方向。
-        // 抓不住：译文对不对（这只能是人工 / 后续的语言审查）。
-        for lang in Lang::ALL {
-            let catalog = Catalog::of(*lang);
-            assert_eq!(catalog.missing(), Vec::new(), "{}", catalog.lang().tag());
-            assert_eq!(catalog.diagnose(), None);
-
-            let mut keys = catalog
-                .entries()
-                .iter()
-                .map(|(key, _)| *key)
-                .collect::<Vec<_>>();
-            let total = keys.len();
-            keys.sort_unstable();
-            keys.dedup();
-            assert_eq!(keys.len(), total, "{} 目录里有重复条目", lang.tag());
-            assert_eq!(
-                keys.len(),
-                Key::ALL.len(),
-                "{} 条目数与 key 数不等",
-                lang.tag()
-            );
-
-            for key in Key::ALL {
-                assert!(
-                    catalog.get(*key).is_some(),
-                    "{} 缺 {}",
-                    lang.tag(),
-                    key.name()
-                );
-            }
-        }
-        assert!(!Key::ALL.is_empty());
-    }
-
-    #[test]
-    fn key_names_are_unique_and_stable() {
-        // 抓得住：同一个 key 被写成两个变体（名字重复会让日志/诊断指认失准）。
-        // 抓不住：重命名变体对下游源码的影响（那是编译错误，本来就跑不过）。
-        let mut names = Key::ALL.iter().map(|key| key.name()).collect::<Vec<_>>();
-        let total = names.len();
-        names.sort_unstable();
-        names.dedup();
-        assert_eq!(names.len(), total);
-        assert_eq!(Key::NavInstances.name(), "NavInstances");
-    }
-
-    #[test]
-    fn chinese_catalog_is_actually_chinese() {
-        // 抓得住：整句漏译（英文被抄进中文表）；一条都没有说明这张表是真翻过的。
-        // 抓不住：语义翻错、语气不合（机器能查的只有「与英文不同」这一层）。
-        let en = Catalog::of(Lang::En);
-        let zh = Catalog::of(Lang::ZhCn);
-        for key in Key::ALL {
-            let english = en.text(*key);
-            assert_ne!(english, zh.text(*key), "{} 未翻译", key.name());
-            assert!(!english.is_empty() && !zh.text(*key).is_empty());
-        }
-    }
-
-    #[test]
-    fn placeholder_sets_match_across_languages() {
-        // 抓得住：一处文案的 `{code}` / `{when}` 在另一套译文里丢了或写错名——
-        //         那会让 render() 输出半截句子，或让参数静默失效。
-        // 抓不住：占位符本身是不是正确的变量（那是调用方的职责，由页面侧测试守）。
-        let en = Catalog::of(Lang::En);
-        let zh = Catalog::of(Lang::ZhCn);
-        for key in Key::ALL {
-            let mut left = placeholders(en.text(*key));
-            let mut right = placeholders(zh.text(*key));
-            left.sort_unstable();
-            right.sort_unstable();
-            assert_eq!(left, right, "{}", key.name());
-        }
-        assert_eq!(placeholders("exit {code} at {when}"), vec!["code", "when"]);
-        assert_eq!(placeholders("没有占位符"), Vec::<&str>::new());
-    }
-
-    #[test]
-    fn missing_rows_are_diagnosed_in_plain_words() {
-        // 抓得住：缺译诊断的**可读性**（必须点名语言、key 名与英文原文）——注入目录缺条时靠它定位。
-        // 抓不住：内置目录真的缺译（内置表由 catalog! 结构保证，见上一条测试）。
-        let partial = Catalog::from_entries(Lang::ZhCn, PARTIAL_ZH);
-        assert_eq!(partial.missing().len(), Key::ALL.len() - PARTIAL_ZH.len());
-
-        let report = partial.diagnose().expect("应当报缺译");
-        assert!(report.starts_with("zh-CN 缺 "), "{report}");
-        assert!(report.contains("LaunchOutcomeSilent"), "{report}");
-        assert!(
-            report.contains("Suspected silent failure"),
-            "诊断要带上英文原文当参考：{report}"
-        );
-        assert!(
-            !report.contains("NavInstances"),
-            "已译的 key 不该出现在报告里：{report}"
-        );
-    }
-
-    #[test]
-    fn missing_translation_never_falls_back_silently() {
-        // 抓得住：缺译被静默顶替（回落英文 / 回落中文 / 返回空串）——那会产出「半句中文半句英文」的界面。
-        // 抓不住：MISSING 标记真的被画到屏幕上（那是 UI 侧截图验收的事）。
-        let partial = Catalog::from_entries(Lang::ZhCn, PARTIAL_ZH);
-        assert_eq!(partial.get(Key::LaunchOutcomeSilent), None);
-        assert_eq!(partial.text(Key::LaunchOutcomeSilent), MISSING);
-        assert_eq!(
-            partial.render(
-                Key::LaunchFailedWithCode,
-                &[("code", "0"), ("reason", "JVM 拒绝启动")]
-            ),
-            "⟪missing:LaunchFailedWithCode⟫"
-        );
-    }
-
-    #[test]
-    fn render_substitutes_and_keeps_unfilled_placeholders_visible() {
-        // 抓得住：占位符替换的回归（漏参时**保留** `{code}` 而不是清空、不 panic）。
-        // 抓不住：调用方传没传对值（`("code", "0")` 是不是真的退出码）。
-        let zh = Catalog::of(Lang::ZhCn);
-        assert_eq!(
-            zh.render(
-                Key::LaunchFailedWithCode,
-                &[("code", "0"), ("reason", "mod 冲突")]
-            ),
-            "启动失败（退出码 0）：mod 冲突"
-        );
-        assert_eq!(
-            zh.render(Key::LaunchFailedWithCode, &[("code", "0")]),
-            "启动失败（退出码 0）：{reason}"
-        );
-        assert_eq!(zh.text(Key::InstancesNew), "新建实例");
-        assert_eq!(zh.lang(), Lang::ZhCn);
-    }
-}
+mod tests;