feat: add CDP connection support for external browsers (#24)

* feat: add CDP connection support for external browsers

Add --cdp flag to connect to browsers via Chrome DevTools Protocol.
This enables control of Electron apps, Chrome instances, or any browser
exposing a CDP endpoint.

- Add cdpPort option to launch command schema
- Implement connectViaCDP() using chromium.connectOverCDP()
- Track browser connection type for proper reconnection handling
- Collect all pages from all contexts for CDP connections

Usage: agent-browser --cdp 9222 snapshot

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* feat: enhance CDP connection handling and improve page tracking

* main.rs update

Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com>

* fix: verify CDP connection is alive before early return in launch()

Prevents misleading errors when the remote browser crashes by checking
isConnected() before reusing an existing browser reference.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix: reconnect when CDP port changes instead of reusing existing browser

Ensures --cdp flag is respected even when a browser session already exists.
Adds tests for launch() reconnection behavior.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Update src/browser.ts

Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com>

* fix: improve CDP connection handling and validation

* feat: add CDP connection validation to ensure browser context accessibility

* Update src/browser.ts

Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com>

* feat: enhance CDP connection handling and add reconnect logic

* fix: improve CDP connection handling during browser closure

* fix: reset cdpPort to null during browser initialization

* feat: enhance browser launch logic to handle CDP connection switching

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com>

README.md

@@ -302,6 +302,7 @@ agent-browser snapshot -i -c -d 5         # Combine options
 | `--name, -n` | Locator name filter |
 | `--exact` | Exact text match |
 | `--headed` | Show browser window (not headless) |
+| `--cdp <port>` | Connect via Chrome DevTools Protocol |
 | `--debug` | Debug output |
 
 ## Selectors
@@ -459,6 +460,25 @@ export async function handler() {
 }
 ```
 
+## CDP Mode
+
+Connect to an existing browser via Chrome DevTools Protocol:
+
+```bash
+# Connect to Electron app
+agent-browser --cdp 9222 snapshot
+
+# Connect to Chrome with remote debugging
+# (Start Chrome with: google-chrome --remote-debugging-port=9222)
+agent-browser --cdp 9222 open about:blank
+```
+
+This enables control of:
+- Electron apps
+- Chrome/Chromium instances with remote debugging
+- WebView2 applications
+- Any browser exposing a CDP endpoint
+
 ## Architecture
 
 agent-browser uses a client-daemon architecture: