refactor: single-user web-based setup — replace env config with Settings UI

Move from multi-user env-var config to single-user web-first architecture:
- Add SetupPage for first-time initialization (replaces /register)
- Add SettingsPage for AI models, exchanges, Telegram, and password management
- Enrich all API route schemas with exact ID usage documentation
- Add PUT /user/password endpoint for in-app password changes
- Remove REGISTRATION_ENABLED, MAX_USERS, TELEGRAM_BOT_TOKEN from env config
- Simplify LoginPage design, remove admin mode and registration links
- Telegram bot now resolves user email for identity display
- start.sh no longer runs interactive Telegram setup

.env.example

@@ -52,10 +52,6 @@ TRANSPORT_ENCRYPTION=false
 # Optional: External Services
 # ===========================================
 
-# Telegram notifications (optional)
-# TELEGRAM_BOT_TOKEN=your-bot-token
-# TELEGRAM_CHAT_ID=your-chat-id
-
 DB_TYPE=postgres
 DB_HOST=10.
 DB_PORT=5432