feat(connect): attach existing tabs + extension connect one-command UX

Completes the zero-confirmation real-Chrome feature.

- Drive the user's EXISTING logged-in tabs (not just newly-created ones):
  extension attachTab now treats "already attached" (a lingering chrome.debugger
  binding after a service-worker restart) as success and announces the tab
  anyway, instead of skipping it. The nm-host also sends {method:"attachAll"}
  when an agent-browser CDP client connects, so the daemon doesn't race an empty
  target list.
- `agent-browser extension connect` auto-discovers the relay's CDP url
  (~/.agent-browser/relay-cdp-url) and attaches — no copying a ws URL. Rewrites
  into the normal `connect <url>` flow; `extension install/status/uninstall`
  unchanged.
- Skill docs: a "drive your real, logged-in Chrome (extension)" section.

Verified end-to-end: `extension connect` listed the user's real tabs (Lark,
LINUX DO, Rakuten, Discord) and read a logged-in Lark doc's title — zero token,
zero confirmation. Full suite 768 passed.

skill-data/core/references/commands.md

@@ -318,6 +318,35 @@ agent-browser --version               # Show version (-V)
 agent-browser <command> --help        # Show detailed help for a command
 ```
 
+## Drive your real, logged-in Chrome (extension — zero confirmation)
+
+Chrome 136 blocked `--remote-debugging-port` on the default profile, so to drive
+the user's *existing* logged-in window, agent-browser uses a Chrome **extension**
+over native messaging — no port, no token, no per-use confirmation (the
+codex/claude approach).
+
+One-time setup:
+```bash
+agent-browser extension install        # writes the native-messaging host manifest
+# then in Chrome: chrome://extensions → Developer mode → Load unpacked →
+#   <repo>/extensions/ab-connect   (load once)
+```
+
+Then, any time:
+```bash
+agent-browser extension connect        # auto-attaches to the live, logged-in tabs
+agent-browser tab                      # list the real tabs it now controls
+agent-browser tab t3                   # switch the session to one of them
+agent-browser snapshot -i / eval / click ...   # drive it like any session
+agent-browser extension status         # is the host installed?
+agent-browser extension uninstall      # remove the host manifest
+```
+
+Security: the extension↔host link is authenticated by Chrome (extension id); the
+host↔agent-browser CDP link uses an unguessable URL in a 0600 file. Use this when
+you need the user's real cookies/login on their actual machine. (`--extension
+<path>` is unrelated — that loads an extension into a *launched* browser.)
+
 ## Debugging
 
 ```bash