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/routes/laya.js

@@ -0,0 +1,42 @@
+const express = require('express');
+const { requireAuth, requireAdmin } = require('../auth');
+const { LayaRequestError, LayaService } = require('../services/layaService');
+
+const router = express.Router();
+const laya = new LayaService();
+
+function sendError(res, error) {
+    const status = error instanceof LayaRequestError ? error.statusCode : 500;
+    const message = error instanceof LayaRequestError ? error.message : 'Internal server error';
+    res.status(status).json({ runtimeAvailable: false, error: message });
+}
+
+router.get('/status', requireAuth, async (req, res) => {
+    res.json(await laya.status());
+});
+
+router.post('/model/download', requireAuth, requireAdmin, async (req, res) => {
+    try {
+        res.json(await laya.downloadModel(req.body?.model));
+    } catch (error) {
+        sendError(res, error);
+    }
+});
+
+router.delete('/model', requireAuth, requireAdmin, async (req, res) => {
+    try {
+        res.json(await laya.deleteModel());
+    } catch (error) {
+        sendError(res, error);
+    }
+});
+
+router.post('/language/batch', requireAuth, async (req, res) => {
+    try {
+        res.json(await laya.detectBatch(req.body));
+    } catch (error) {
+        sendError(res, error);
+    }
+});
+
+module.exports = router;