feat(pi-dosbox): persistent DOSBox with QBasic and agent tool

- DOSBox now starts at session_start and persists in background
- /dosbox command attaches UI to running instance (Ctrl+Q detaches)
- Added dosbox tool with actions: send_keys, screenshot, read_text
- Bundled QuickBASIC 4.5 files, mounted at C:\QB on startup
- Agent can interact with DOSBox programmatically via tool

Use: pi -e ./examples/extensions/pi-dosbox
Then: /dosbox to view, or let agent use the dosbox tool

packages/coding-agent/examples/extensions/pi-dosbox/package.json

@@ -4,7 +4,6 @@
   "version": "0.0.1",
   "type": "module",
   "scripts": {
-    "start": "npx tsx src/main.ts",
     "clean": "echo 'nothing to clean'",
     "build": "echo 'nothing to build'",
     "check": "echo 'nothing to check'"