feat: cache manager and webapp manifest repository

app/src/main/java/top/yeij/hearth/cache/CacheManager.kt

@@ -0,0 +1,18 @@
+package top.yeij.hearth.cache
+
+import java.io.File
+
+// 文件缓存：以 key 为文件名，内容以 UTF-8 纯文本落盘
+// File cache: uses key as filename, content stored as UTF-8 plain text
+class CacheManager(private val baseDir: File) {
+    init { baseDir.mkdirs() }
+
+    fun save(key: String, content: String) {
+        File(baseDir, key).writeText(content)
+    }
+
+    fun load(key: String): String? {
+        val f = File(baseDir, key)
+        return if (f.exists()) f.readText() else null
+    }
+}

app/src/main/java/top/yeij/hearth/webapp/WebAppRepository.kt

@@ -0,0 +1,51 @@
+package top.yeij.hearth.webapp
+
+import com.google.gson.Gson
+import top.yeij.hearth.cache.CacheManager
+
+// Web 应用清单条目
+// Web app manifest entry
+data class WebApp(val id: String, val name: String, val icon: String, val url: String)
+
+// 网络抽象接口：Task 10 的 CardRepository 也会复用
+// HTTP abstraction reused by Task 10 CardRepository
+interface HttpClient {
+    fun get(url: String): String?
+}
+
+// 清单拉取仓库：拉取成功缓存 body 并解析；失败回退缓存；无缓存返回空列表
+// Manifest repository: on success cache + parse; on failure fall back to cache; no cache -> empty list
+class WebAppRepository(
+    private val http: HttpClient,
+    private val cache: CacheManager,
+    private val manifestUrl: String,
+) {
+    private val gson = Gson()
+
+    fun fetchManifest(): List<WebApp> {
+        val body = http.get(manifestUrl)
+        if (body != null) {
+            cache.save(KEY, body)
+            return parse(body)
+        }
+        val cached = cache.load(KEY) ?: return emptyList()
+        return parse(cached)
+    }
+
+    private fun parse(body: String): List<WebApp> {
+        val root = gson.fromJson(body, Map::class.java)
+        val apps = root["apps"] as? List<*> ?: return emptyList()
+        return apps.mapNotNull { m ->
+            val map = m as? Map<*, *> ?: return@mapNotNull null
+            val id = map["id"] as? String ?: return@mapNotNull null
+            val name = map["name"] as? String ?: return@mapNotNull null
+            val icon = map["icon"] as? String ?: return@mapNotNull null
+            val url = map["url"] as? String ?: return@mapNotNull null
+            WebApp(id, name, icon, url)
+        }
+    }
+
+    companion object {
+        private const val KEY = "webapp-manifest"
+    }
+}