refactor: supprimer complètement les matrices de routing inputToGroup/groupToOutput

Le paradigme devient : pour brancher un canal physique sur un groupe,
créer un server audio user. Les matrices sont retirées de l'UI Electron,
de l'admin PWA, de l'API REST et du backend (GroupAudioRouter supprimé).
AudioBridgeManager ne génère plus de tokens per-group.
Option "aucune sortie" ajoutée pour les server audio users.

server/api/admin.js

@@ -529,66 +529,6 @@ router.put('/audio/channels/names', (req, res) => {
   }
 });
 
-/**
- * GET /admin/audio/routing
- * Récupère la configuration de routing actuelle
- * Format: { inputToGroup: { "0": ["production"], "1": ["technique"] }, groupToOutput: { "production": ["0", "1"] } }
- */
-router.get('/audio/routing', (req, res) => {
-  try {
-    const config = configManager.get();
-    const routing = config.audio?.routing || { inputToGroup: {}, groupToOutput: {}, gains: {} };
-
-    res.json({
-      routing
-    });
-  } catch (error) {
-    console.error('Erreur GET /admin/audio/routing:', error);
-    res.status(500).json({ error: 'Failed to load routing' });
-  }
-});
-
-/**
- * POST /audio/routing
- * Sauvegarde la configuration de routing
- * Body: { inputToGroup: {...}, groupToOutput: {...}, gains: {...} }
- */
-router.post('/audio/routing', (req, res) => {
-  try {
-    const { inputToGroup, groupToOutput, gains } = req.body;
-
-    const config = configManager.get();
-
-    if (!config.audio.routing) {
-      config.audio.routing = { inputToGroup: {}, groupToOutput: {}, gains: {} };
-    }
-
-    if (inputToGroup !== undefined) {
-      config.audio.routing.inputToGroup = inputToGroup;
-    }
-
-    if (groupToOutput !== undefined) {
-      config.audio.routing.groupToOutput = groupToOutput;
-    }
-
-    if (gains !== undefined) {
-      config.audio.routing.gains = gains;
-    }
-
-    configManager.save(config);
-
-    addLog('info', 'Audio routing updated');
-
-    res.json({
-      message: 'Audio routing updated',
-      routing: config.audio.routing
-    });
-
-  } catch (error) {
-    console.error('Erreur POST /admin/audio/routing:', error);
-    res.status(500).json({ error: 'Failed to update routing' });
-  }
-});
 
 /**
  * POST /admin/audio/device