feat: add optional Laya engine mode for grouping and language detection (#12)

Add a languageDetectionMode setting (algo | laya | laya+algo) exposed
in Settings with three engine choices. When Laya is enabled, a laya
service (Dockerfile.laya, optional compose profile, models stored
outside the repo under ./data/models/laya) can be started, with model
download and deletion from the UI via /laya routes to manage disk
space. Add a channelLanguageFusion service combining Laya results
with the existing algorithm, and wire detection mode through
grouping, channel list and player. Cover engine selection, fusion
and laya service behavior with tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/db/sqlite.js

@@ -135,6 +135,18 @@ function initSchema() {
         CREATE INDEX IF NOT EXISTS idx_history_user_item ON watch_history(user_id, item_id);
     `);
 
+    db.exec(`
+        CREATE TABLE IF NOT EXISTS laya_language_cache (
+            cache_key TEXT PRIMARY KEY,
+            mode TEXT NOT NULL,
+            model TEXT NOT NULL,
+            response TEXT NOT NULL,
+            created_at INTEGER NOT NULL
+        );
+        CREATE INDEX IF NOT EXISTS idx_laya_cache_mode_model
+            ON laya_language_cache(mode, model);
+    `);
+
     // Migration: Add source_id column if missing (for existing databases)
     try {
         db.exec(`ALTER TABLE watch_history ADD COLUMN source_id INTEGER`);
@@ -209,8 +221,32 @@ const favorites = {
     }
 };
 
+const layaLanguageCache = {
+    get(cacheKey) {
+        const row = getDb().prepare(
+            'SELECT response FROM laya_language_cache WHERE cache_key = ?'
+        ).get(cacheKey);
+        return row ? JSON.parse(row.response) : null;
+    },
+
+    set(cacheKey, mode, model, response) {
+        getDb().prepare(`
+            INSERT INTO laya_language_cache (cache_key, mode, model, response, created_at)
+            VALUES (?, ?, ?, ?, ?)
+            ON CONFLICT(cache_key) DO UPDATE SET
+                response = excluded.response,
+                created_at = excluded.created_at
+        `).run(cacheKey, mode, model, JSON.stringify(response), Date.now());
+    },
+
+    clear() {
+        getDb().prepare('DELETE FROM laya_language_cache').run();
+    }
+};
+
 module.exports = {
     getDb,
     initSchema,
-    favorites
+    favorites,
+    layaLanguageCache
 };