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.

cli/Cargo.lock

@@ -290,7 +290,7 @@ checksum = "613afe47fcd5fac7ccf1db93babcb082c5994d996f20b8b159f2ad1658eb5724"
 
 [[package]]
 name = "chrome-use"
-version = "1.5.19"
+version = "1.5.20"
 dependencies = [
  "aes",
  "aes-gcm",