revert: default icon prefix back to github raw

Prefer github as default; the self-hosted Gitea (now at
https://git.sunlunfan.com) stays available as a manually-entered
alternative. Drops the github->gitea migration added earlier.

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

app/src/main/java/com/a2i/forwarder/store/SettingsStore.kt

@@ -94,16 +94,7 @@ class SettingsStore(
                 _servers.value = list
                 _currentServerId.value = p[K.CURRENT] ?: ID_OFFICIAL
                 currentServer.value = list.firstOrNull { it.id == _currentServerId.value } ?: list.firstOrNull()
-                // 图标前缀：旧 github 默认值自动迁移到 Gitea；用户自定义值保留
-                val storedPrefix = p[K.ICON_PREFIX]
-                iconPrefix.value = when (storedPrefix) {
-                    null -> DEFAULT_ICON_PREFIX
-                    LEGACY_ICON_PREFIX -> {
-                        scope.launch { edit { it[K.ICON_PREFIX] = DEFAULT_ICON_PREFIX } }
-                        DEFAULT_ICON_PREFIX
-                    }
-                    else -> storedPrefix
-                }
+                iconPrefix.value = p[K.ICON_PREFIX] ?: DEFAULT_ICON_PREFIX
                 forwardingEnabled.value = p[K.FWD] ?: true
                 codeEnabled.value = p[K.CODE] ?: true
                 adFilterEnabled.value = p[K.AD] ?: true
@@ -193,8 +184,6 @@ class SettingsStore(
 
     companion object {
         const val ID_OFFICIAL = "official"
-        // 图标前缀默认走自建 Gitea（国内可达）；github raw 作为备份
-        const val DEFAULT_ICON_PREFIX = "http://45.143.131.159:3000/song/a2i/raw/branch/main/icons/"
-        const val LEGACY_ICON_PREFIX = "https://raw.githubusercontent.com/lsxf/a2i/main/icons/"
+        const val DEFAULT_ICON_PREFIX = "https://raw.githubusercontent.com/lsxf/a2i/main/icons/"
     }
 }