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/daemon/embedded_daemon.cpp

@@ -1,6 +1,9 @@
 // DragonX Wallet - ImGui Edition
 // Copyright 2024-2026 The Hush Developers
 // Released under the GPLv3
+//
+// embedded_daemon.cpp — Manages the dragonxd child process lifecycle:
+// binary discovery, process spawn, stdout/stderr monitoring, crash recovery.
 
 #include "embedded_daemon.h"
 #include "../config/version.h"

src/daemon/xmrig_manager.cpp

@@ -1,6 +1,9 @@
 // DragonX Wallet - ImGui Edition
 // Copyright 2024-2026 The Hush Developers
 // Released under the GPLv3
+//
+// xmrig_manager.cpp — Pool mining process management via xmrig-hac.
+// Spawns xmrig, monitors via HTTP API, tracks hashrate and shares.
 
 #include "xmrig_manager.h"
 #include "../resources/embedded_resources.h"