feat(app-iced): M68 —— iced 0.14 骨架（后端探测/字体基座/自绘标题栏/导航轨/深浅主题/截图通道）

新增 crates/app-iced（package `unlucky-app-iced`，bin `unlucky-launcher-iced`），与 Slint 版并存，
为 D26「UI 从头写」打地基。本 mission 只做骨架：能开窗、颜色/字体对、层级在，不做业务页面。

- 后端（D27）：启动探测 wgpu 适配器（只看 device_type，避开 WARP 误判）→ 写 ICED_BACKEND；
  auto/gpu/cpu 三条路径都保留 tiny-skia 兜底，绝不硬失败；`--renderer=cpu` 跳过探测（省 ~0.85s）
- 字体（D28 前半）：令牌三平台字体栈 → 用 iced 全局 FontSystem 查装机情况 → 族名与 400/500/700
  字重落点（缺档按 Nearest/Synthetic 记录）打一行启动日志
- 令牌适配层 theme::Ui：唯一把 unlucky-design 的值翻成 iced Color/Font/Border/Radius/Theme 的地方；
  49 个 M3 角色留在自己的 Scheme 里，iced 的 6 色 Palette 只给 devtools
- 骨架：1180×760 无边框窗口、48 高自绘标题栏（drag + 东/南 drag_resize + 最小化/最大化/关闭）、
  88 宽导航轨（56×32 SecondaryContainer 药丸，由令牌推导）、页头 56 + 一张 OutlinedCard
- 主题：系统主题探测 + --theme，切主题只重建 Ui（Theme::name 变化触发重算），不动 UI 状态
- 截图通道：`--screenshot <png>` + `--screenshot-theme`（真开窗第 3 帧出图），以及
  `--diff <a> <b>` 自带逐像素对比（CI 不依赖 Python/ImageMagick）
- 图标：令牌 SVG path → iced svg 控件（颜色走 alpha 蒙版，深浅共用一份位图缓存）
- 门禁：tests/no_hardcoded_tokens.rs 扫源码挡色值/尺寸字面量 + 挡 slint 依赖（自检也算过）

实测（Windows Server 2025 / 96 DPI / RX 6600 XT）：浅/深 × GPU/CPU 四张真开窗截图；GPU vs CPU
差异 0.72% 像素、全部落在字形/图标抗锯齿与 1px 圆角描边、最佳对齐 (0,0)、平坦区颜色逐字节相同；
release 体积双后端 6.44 MiB / 仅 CPU 3.75 MiB；首帧 GPU 1.18~1.31s、CPU 33~37ms。

未做/未验证：macOS 与 Wayland 全链路、西/北边缩放热区、letter spacing（iced 0.14 无此属性）、
中文 CDN 字体、玻璃；翻牌步骤写在 DevDocs/SubAgentsTalk/app-iced-骨架与翻牌.md（不入库）。

crates/app-iced/src/fonts/tests.rs

@@ -0,0 +1,163 @@
+//! `fonts` 的单元测试（拆出来只为「src 文件 ≤400 行」的门禁）。
+
+use super::*;
+use unlucky_design::typography::WeightCoverage;
+
+fn only(installed: &'static [&'static str]) -> impl Fn(&str) -> bool {
+    move |family| installed.contains(&family)
+}
+
+#[test]
+fn windows_stack_falls_back_to_classic_segoe_when_variable_is_absent() {
+    // Win10 没有 Segoe UI Variable Text
+    let family = pick(
+        Platform::Windows,
+        FontFamily::Text,
+        &only(&["Segoe UI", "Microsoft YaHei UI"]),
+    );
+    assert_eq!(family, "Segoe UI");
+}
+
+#[test]
+fn windows_stack_prefers_the_variable_face_on_win11() {
+    let family = pick(
+        Platform::Windows,
+        FontFamily::Text,
+        &only(&["Segoe UI Variable Text", "Segoe UI"]),
+    );
+    assert_eq!(family, "Segoe UI Variable Text");
+}
+
+#[test]
+fn generic_family_names_are_never_reported_as_the_resolved_family() {
+    // 一个都没装：返回栈头，且栈头不是通用族名
+    let family = pick(Platform::Linux, FontFamily::Text, &only(&[]));
+    assert_eq!(family, "Roboto");
+    assert!(!is_generic(family));
+}
+
+#[test]
+fn missing_cjk_fonts_do_not_change_the_latin_pick() {
+    // 装了苹方但没装 SF：macOS 栈应该选 Helvetica Neue 而不是中文族
+    let family = pick(
+        Platform::MacOs,
+        FontFamily::Text,
+        &only(&["PingFang SC", "Helvetica Neue"]),
+    );
+    assert_eq!(family, "Helvetica Neue");
+}
+
+#[test]
+fn weight_reports_use_the_token_degradation_path() {
+    // 没有系统字面表时回落到令牌纯函数：Windows 栈里 Segoe UI Variable Text 是可变 300..700
+    let medium = weight_report(
+        Platform::Windows,
+        "Segoe UI Variable Text",
+        Weight::Medium,
+        None,
+    );
+    assert_eq!(medium.requested, 500);
+    assert_eq!(medium.quality, WeightMatch::Native);
+
+    // 手工构造一个「只有 400/700」的族（= 经典 Segoe UI），500 应该落到最近档
+    let faces = [
+        Face {
+            family: "Segoe UI".to_owned(),
+            weight: 400,
+        },
+        Face {
+            family: "Segoe UI".to_owned(),
+            weight: 700,
+        },
+    ];
+    let medium = weight_report(Platform::Windows, "Segoe UI", Weight::Medium, Some(&faces));
+    assert_eq!(medium.available, 400, "400 比 700 更近");
+    assert_eq!(medium.quality, WeightMatch::Nearest);
+
+    // 只有 400 却要 700 → 合成加粗
+    let only_regular = [Face {
+        family: "Narrow".to_owned(),
+        weight: 400,
+    }];
+    let bold = weight_report(
+        Platform::Windows,
+        "Narrow",
+        Weight::Bold,
+        Some(&only_regular),
+    );
+    assert_eq!(bold.quality, WeightMatch::Synthetic);
+
+    // 原生有 500 就用 500
+    let has_medium = [Face {
+        family: "Noto".to_owned(),
+        weight: 500,
+    }];
+    assert_eq!(
+        weight_report(Platform::Linux, "Noto", Weight::Medium, Some(&has_medium)).quality,
+        WeightMatch::Native
+    );
+
+    let narrow = WeightCoverage::Static(&[400]);
+    assert_eq!(narrow.nearest(700), 400);
+}
+
+#[test]
+fn describe_is_one_line_and_mentions_all_three_stacks() {
+    let resolved = Resolved {
+        platform: Platform::Windows,
+        families: [
+            FamilyReport {
+                stack: "text",
+                family: "Segoe UI",
+                installed: true,
+            },
+            FamilyReport {
+                stack: "display",
+                family: "Segoe UI Variable Display",
+                installed: false,
+            },
+            FamilyReport {
+                stack: "mono",
+                family: "Cascadia Mono",
+                installed: true,
+            },
+        ],
+        weights: [
+            WeightReport {
+                requested: 400,
+                available: 400,
+                quality: WeightMatch::Native,
+            },
+            WeightReport {
+                requested: 500,
+                available: 400,
+                quality: WeightMatch::Nearest,
+            },
+            WeightReport {
+                requested: 700,
+                available: 400,
+                quality: WeightMatch::Synthetic,
+            },
+        ],
+    };
+
+    let line = resolved.describe();
+    assert_eq!(line.lines().count(), 1);
+    assert!(line.contains("text=\"Segoe UI\""), "{line}");
+    assert!(line.contains("未装机"), "{line}");
+    assert!(line.contains("w700=400(synthetic)"), "{line}");
+    assert!(resolved.has_synthetic());
+    assert_eq!(resolved.families().text, "Segoe UI");
+}
+
+#[test]
+fn type_roles_pick_the_display_stack_for_big_text() {
+    use unlucky_design::typography::TypeRole;
+
+    assert_eq!(
+        TypeRole::TitleLarge.style().family,
+        FontFamily::Display,
+        "22px 标题走 Display 栈"
+    );
+    assert_eq!(TypeRole::BodyMedium.style().family, FontFamily::Text);
+}