feat(site): auto-sync + auto-suggest adapters (auto-trigger)

Make `site` trigger itself so an agent doesn't have to know adapters exist.

Auto-sync: the pack refreshes on first use and on a TTL (default 7d), both in
the `site` command path (blocking, fast) and as a non-blocking background task
on daemon startup — so ~/.chrome-use/sites/.index.json is always populated with
zero added latency. Tune via AGENT_BROWSER_SITES_TTL_DAYS; disable with
AGENT_BROWSER_SITES_NO_AUTO_UPDATE=1. `update` now writes .last_update + a
domain→adapters .index.json (read-only adapters ordered first).

Auto-suggest: `open`/`navigate`/`snapshot` onto a domain with adapters attaches
`siteAdapters: {domain, commands}` to the response; the CLI prints a
`💡 site adapters for <domain>` hint (stderr) and the field rides along in --json.
SKILL.md tells the agent to prefer the listed `site <name>/<cmd>` over scraping.
This keeps the 'never auto-disrupt user tabs' guarantee — it suggests, the agent
decides; nothing auto-runs on navigation.

site.rs: needs_refresh/adapters_for_domain/write_domain_index + timestamp/index
in update(). daemon.rs: background bootstrap. actions.rs: with_site_hint on
navigate + snapshot. output.rs: hint render. Verified live: open github.com →
hint leads with read-only github/issues; --json carries siteAdapters.

README.md

@@ -233,6 +233,22 @@ Positional args fill the adapter's declared args in order; `--key value` overrid
 by name. Adapters are authored by the bb-sites community and remain their authors'
 property — chrome-use just runs them.
 
+**Auto-sync + auto-suggest.** You rarely type `site update` yourself: chrome-use
+syncs the pack on first use and refreshes it weekly in the background (tune with
+`AGENT_BROWSER_SITES_TTL_DAYS`, disable with `AGENT_BROWSER_SITES_NO_AUTO_UPDATE=1`).
+And when you `open`/`snapshot` a page whose domain has adapters, chrome-use surfaces
+them right in the output — a `💡 site adapters for <domain>` line, plus a
+`siteAdapters` field under `--json` — so an agent reaches for the structured-data
+adapter instead of scraping the DOM:
+
+```text
+$ chrome-use open https://github.com
+💡 site adapters for github.com — prefer these for structured data:
+   github/issues, github/me, github/repo, …
+   e.g. chrome-use site github/issues --json
+✓ GitHub
+```
+
 ## Automated testing (`chrome-use test`)
 
 Turn the repetitive "open it, click around, check it's right" work into a