fix: loyalty tier crash, chat duplicate rooms, sidebar defaults

- LoyaltyPage: levelBadge() now falls back to bronze for unknown tiers
  (DB had loyalty_tier='standard' from old seed data)
- migration 040: deduplicate general chat rooms + add unique index,
  normalize loyalty_tier to bronze for non-standard values
- chat.ts: ON CONFLICT clause now targets the new partial unique index
- Sidebar: DEFAULT_GROUPS only opens 'basics' by default; bump
  localStorage key to sidebarGroups_v2 to clear stale stored state

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/routes/chat.ts

@@ -18,7 +18,7 @@ const chatRoutes: FastifyPluginAsync = async (fastify) => {
     const { rows } = await db.query(
       `INSERT INTO chat_rooms (hotel_id, type, name)
        VALUES ($1, 'general', 'Общий чат')
-       ON CONFLICT DO NOTHING
+       ON CONFLICT (hotel_id) WHERE type = 'general' DO NOTHING
        RETURNING id`,
       [hotelId],
     )