feat(live): add language-aware flexible channel search (#23)

Add backend language detection, flexible live channel search, iptv-org catalog caching, and protected built-in EPG source registration.

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

server/routes/sources.js

@@ -93,6 +93,9 @@ router.put('/:id', async (req, res) => {
         }
 
         const { name, url, username, password } = req.body;
+        if (existing.builtinKey) {
+            return res.status(409).json({ error: 'Built-in sources can only be enabled or disabled', code: 'BUILTIN_SOURCE_READONLY' });
+        }
         const updated = await sources.update(req.params.id, {
             name: name || existing.name,
             url: url || existing.url,
@@ -116,6 +119,9 @@ router.delete('/:id', async (req, res) => {
         if (!existing) {
             return res.status(404).json({ error: 'Source not found' });
         }
+        if (existing.builtinKey) {
+            return res.status(409).json({ error: 'Built-in sources cannot be removed', code: 'BUILTIN_SOURCE_PROTECTED' });
+        }
 
         // Cascade delete: Clean up SQLite data for this source
         const db = getDb();