Refactor networking to use Network.framework

Replace MultipeerConnectivity with a custom P2P implementation using Network.framework (NWListener/NWConnection) and CoreBluetooth for discovery.
- Add P2PConnectionManager, BLEDiscoveryManager, and NetworkFraming.
- Add ConnectedPeer and DiscoveredHost models.
- Update Info.plist with local network and bluetooth permissions.
- Refactor Views to use P2PConnectionManager.
- Add implementation plan and transition docs.

.claude/settings.local.json

@@ -0,0 +1,10 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(git add:*)",
+      "Bash(git commit:*)",
+      "Bash(git push:*)",
+      "Bash(./check_build.sh:*)"
+    ]
+  }
+}