Add scheduler improvements, API endpoints, and month calendar view

Backend:
- Add /api/customers/ endpoint (CustomerViewSet, CustomerSerializer)
- Add /api/services/ endpoint with Service model and migrations
- Add Resource.type field (STAFF, ROOM, EQUIPMENT) with migration
- Fix EventSerializer to return resource_id, customer_id, service_id
- Add date range filtering to EventViewSet (start_date, end_date params)
- Add create_demo_appointments management command
- Set default brand colors in business API

Frontend:
- Add calendar grid view for month mode in OwnerScheduler
- Fix sidebar navigation active link contrast (bg-white/10)
- Add default primaryColor/secondaryColor fallbacks in useBusiness
- Disable WebSocket (backend not implemented) to stop reconnect loop
- Fix Resource.type.toLowerCase() error by adding type to backend

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/test-results/.last-run.json

@@ -1,8 +1,6 @@
 {
   "status": "failed",
   "failedTests": [
-    "5f1889fdd7b10a4db9e9-2b1e81c51a733cc89956",
-    "5f1889fdd7b10a4db9e9-66724cc37c12aaf9dc66",
-    "5f1889fdd7b10a4db9e9-b93c630b7987c0eb4adc"
+    "7662eeffef95b745c0c7-05f7d22eaed6ca80a04d"
   ]
 }