fix: discover Gitea update source from release notes (no hardcode)

Gitea URL removed from source code. UpdateChecker now only hardcodes
GitHub API; the Gitea mirror URL is embedded in release notes as an
HTML comment (<!-- update-source: ... -->) and discovered at runtime.
Keeps self-hosted server address out of the public codebase.

version 1.8.0 -> 1.8.1 (code 17 -> 18)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/main/java/com/a2i/forwarder/core/UpdateChecker.kt

@@ -68,9 +68,14 @@ class UpdateChecker(private val context: Context) {
             val now = System.currentTimeMillis()
             if (throttle && now - settings.lastUpdateCheckTime.value < CHECK_INTERVAL_MS) return@runCatching updateInfo.value
 
-            // 双源查询（Gitea 国内优先 + GitHub 备用），任一不通跳过，取最高版本
-            val infos = RELEASES_APIS.mapNotNull { api ->
-                runCatching { fetchRelease(api) }.getOrNull()
+            // 先查 GitHub（公开默认源），从其 release notes 动态发现额外源（如自建 Gitea），取最高版本
+            val infos = mutableListOf<UpdateInfo>()
+            val gh = runCatching { fetchRelease(GITHUB_API) }.getOrNull()
+            if (gh != null) {
+                infos.add(gh)
+                parseUpdateSource(gh.releaseNotes)?.let { src ->
+                    runCatching { fetchRelease(src) }.getOrNull()?.let { infos.add(it) }
+                }
             }
             settings.setLastUpdateCheck(now)
             if (infos.isEmpty()) {
@@ -245,12 +250,12 @@ class UpdateChecker(private val context: Context) {
         return false
     }
 
+    /** 从 release notes 的 HTML 注释里解析额外更新源（如自建 Gitea）。 */
+    private fun parseUpdateSource(body: String): String? =
+        Regex("""update-source:\s*(\S+)""").find(body)?.groupValues?.getOrNull(1)
+
     companion object {
-        // 双源：Gitea（国内优先）+ GitHub（备用），任一不通跳过，取最高版本
-        val RELEASES_APIS = listOf(
-            "https://UPDATE_SOURCE_HIDDEN/api/v1/repos/song/a2i/releases/latest",
-            "https://api.github.com/repos/lsxf/a2i/releases/latest",
-        )
+        const val GITHUB_API = "https://api.github.com/repos/lsxf/a2i/releases/latest"
         const val CHECK_INTERVAL_MS = 24L * 60 * 60 * 1000
     }