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/db.js

@@ -1,6 +1,7 @@
 const fs = require('fs/promises');
 const path = require('path');
 const { existsSync, mkdirSync } = require('fs');
+const { ensureBuiltinSources } = require('./services/builtinEpgRegistry');
 
 // Ensure data directory exists (sync is fine for startup)
 const dataDir = path.join(__dirname, '..', 'data');
@@ -17,25 +18,25 @@ async function loadDb() {
     try {
       const fileContent = await fs.readFile(dbPath, 'utf-8');
       const data = JSON.parse(fileContent);
-      return {
+      return ensureBuiltinSources({
         sources: data.sources || [],
         hiddenItems: data.hiddenItems || [],
         favorites: data.favorites || [],
         settings: data.settings || getDefaultSettings(),
         users: data.users || [],
         nextId: data.nextId || 1
-      };
+      });
     } catch (error) {
       if (error.code === 'ENOENT') {
         // File doesn't exist, return default
-        return {
+        return ensureBuiltinSources({
           sources: [],
           hiddenItems: [],
           favorites: [],
           settings: getDefaultSettings(),
           users: [],
           nextId: 1
-        };
+        });
       }
       throw error;
     }
@@ -168,6 +169,11 @@ const sources = {
     const index = db.sources.findIndex(s => s.id === parseInt(id));
     if (index === -1) return null;
 
+    const existing = db.sources[index];
+    if (existing.builtinKey) {
+      const allowed = Object.keys(updates).every(key => key === 'enabled');
+      if (!allowed) throw Object.assign(new Error('Built-in sources can only be enabled or disabled'), { code: 'BUILTIN_SOURCE_READONLY' });
+    }
     db.sources[index] = {
       ...db.sources[index],
       ...updates,
@@ -179,6 +185,8 @@ const sources = {
 
   async delete(id) {
     const db = await loadDb();
+    const existing = db.sources.find(s => s.id === parseInt(id));
+    if (existing?.builtinKey) throw Object.assign(new Error('Built-in sources cannot be removed'), { code: 'BUILTIN_SOURCE_PROTECTED' });
     db.sources = db.sources.filter(s => s.id !== parseInt(id));
     // Also delete related hidden items and favorites
     db.hiddenItems = db.hiddenItems.filter(h => h.source_id !== parseInt(id));