feat: smart LAN/tunnel URL switching for remote connections

[jfversluis]

Problem

When connecting a mobile device to a desktop PolyPilot server, users must choose between a LAN address (fast, only works on same network) or a DevTunnel URL (works everywhere, slower). If the user scans a LAN QR code and then leaves the house, the connection breaks with no fallback.

Solution

The app now stores both URLs and automatically picks the best one:

How it works

1. QR codes encode both URLs when both sharing modes are active (DevTunnel + Direct Connection)
2. At connect time, the app probes the LAN address first (2-second HTTP timeout):
   • ✅ LAN reachable → use fast local connection
   • ❌ LAN unreachable → fall back to tunnel
   • 📱 On cellular (no WiFi) → skip LAN probe entirely, use tunnel
3. On reconnect, re-resolves which URL to use — network may have changed
4. Connectivity monitoring (iOS/Android) — debounced MAUI Connectivity.ConnectivityChanged events detect WiFi↔cellular transitions

New fields

Field	Purpose
ConnectionSettings.LanUrl	LAN server address (e.g., http://192.168.1.5:4322)
ConnectionSettings.LanToken	Server password for LAN auth

QR code format (backward compatible)

{
  "url": "https://xxx.devtunnels.ms",
  "token": "tunnel-jwt",
  "lanUrl": "http://192.168.1.5:4322",
  "lanToken": "server-password"
}

Old QR codes without lanUrl continue to work — single-URL mode, no probing overhead.

Edge cases handled

Scenario	Behavior
Only LAN, no tunnel	Uses LAN directly, no probe
Only tunnel, no LAN	Uses tunnel directly, no probe
LAN IP changed	2s probe fails → tunnel fallback
WiFi → cellular	Reconnect re-resolves to tunnel
Cellular → WiFi	Reconnect probes LAN first

Files changed (9 files)

• ConnectionSettings.cs — LanUrl/LanToken properties
• WsBridgeClient.cs — ConnectSmartAsync, ResolveUrlAsync, ProbeLanAsync, IsCellularOnly
• IWsBridgeClient.cs — new interface methods
• CopilotService.Bridge.cs — ToWebSocketUrl helper, smart connect routing, connectivity monitor
• CopilotService.cs — accept LanUrl-only configs
• Dashboard.razor — parse/save LanUrl from QR scan
• Settings.razor — QR generation includes both URLs, validation accepts LanUrl
• TestStubs.cs — stub updates
• SmartUrlResolutionTests.cs — 25 new tests

Tests

All 1169 tests pass (25 new + 1144 existing). 1 pre-existing locale-dependent failure unrelated.