change background.js into split typescript files for better managemand and build background.js from typescript

README.md

@@ -95,8 +95,9 @@ browser-cli/
 │       └── session.py     # session save/load
 ├── extension/
 │   ├── manifest.json      # MV3 extension manifest
-│   ├── background.js      # Service worker command dispatcher
-│   └── content.js         # Content-script helpers
+│   ├── content.js         # Content-script helpers
+│   └── src/               # TypeScript source split by command area
+│       └── index.ts       # Builds generated extension/background.js
 ├── examples/
 │   ├── demo.py            # Python API walkthrough
 │   └── demo.sh            # Bash CLI walkthrough
@@ -402,6 +403,18 @@ bash examples/demo.sh
 
 ---
 
+## Development
+
+```sh
+npm ci
+npm run check:extension   # type-check, build extension/background.js, syntax-check bundle
+uv run pytest -q
+```
+
+The extension source lives in `extension/src/`. `extension/background.js` is generated and ignored by git. Run `npm run build:extension` before using `Load unpacked` with `extension/`.
+
+---
+
 ## Limitations
 
 - **Browser internal pages** (`chrome://`, `brave://`, `edge://`, `about:`) cannot be scripted. DOM and extract commands only work on regular `http://` and `https://` pages.