fix: WebSocket reconnection stability and manual pairing flow

[comlibmb]

Summary

Fixes for WebSocket reconnection after tunnel restart and manual pairing code flow.

Changes

1. WebSocket Service (services/websocket.service.ts)

   • pollTunnelUrl polls Supabase every 10s, detects tunnel URL change and auto-reconnects
   • Limit Socket.IO auto-reconnect attempts to 3 (was Infinity) to prevent conflicts
   • Remove checkTunnelUrlOnDisconnect (was conflicting with poll mechanism)

2. App Layout (app/_layout.tsx)

   • AppState foreground handler always checks tunnel URL vs current relay URL
   • Reconnects if URL changed or connection lost

3. Add Device (app/(onboarding)/add-device.tsx)

   • "Enter Code" mode now redirects to device/pair.tsx for reliable pairing

4. Pair Device (app/device/pair.tsx)

   • Support ?method=code query param to pre-select "Enter Code" mode

Bug Fixes

• Mobile stuck on "Connecting to server..." after tunnel restart (race condition between multiple reconnect mechanisms)
• Manual pairing code on Add Device page always failed (relay address was required)
• add-device.tsx showed "Relay Address Required" dialog even in tunnel mode

Test Plan

• Kill cloudflared → mobile auto-reconnects within ~10s
• App foreground/background reconnect works
• Manual pairing code on Add Device page works
• QR scan pairing works
• Sessions usable after reconnect