docs: add copilot-instructions.md and file-level comments

- Create .github/copilot-instructions.md with project coding standards,
  architecture overview, threading model, and key rules for AI sessions
- Add module description comments to app.cpp, rpc_client.cpp, rpc_worker.cpp,
  embedded_daemon.cpp, xmrig_manager.cpp, console_tab.cpp, settings.cpp
- Add ASCII connection state diagram to app_network.cpp
- Remove /.github/ from .gitignore so instructions file is tracked

src/app_network.cpp

@@ -2,8 +2,32 @@
 // Copyright 2024-2026 The Hush Developers
 // Released under the GPLv3
 //
-// app_network.cpp — RPC connection, data refresh, and network operations
+// app_network.cpp — RPC connection, data refresh, and network operations.
 // Split from app.cpp for maintainability.
+//
+// Connection state machine:
+//
+//   [Disconnected]
+//        │
+//        ▼  tryConnect() every 5s
+//   Auto-detect DRAGONX.conf (host, port, rpcuser, rpcpassword)
+//        │
+//        ├─ no config found ──► start embedded daemon ──► retry
+//        │
+//        ▼  post async rpc_->connect() to worker_
+//   [Connecting]
+//        │
+//        ├─ success ──► onConnected()  ──► [Connected]
+//        │                                     │
+//        │                                     ▼  refreshData() every 5s
+//        │                                  [Running]
+//        │                                     │
+//        │                                     ├─ RPC error ──► onDisconnected()
+//        │                                     │                     │
+//        ├─ auth 401 ──► .cookie auth ──► retry│                     ▼
+//        │                                     │              [Disconnected]
+//        └─ failure ──► onDisconnected(reason) ┘
+//                       may restart daemon
 
 #include "app.h"
 #include "rpc/rpc_client.h"