feat(find-url): search local Chrome/Edge bookmarks by keyword

Borrow web-access's find-url: locate an internal system or a previously-saved
page that public search can't reach, without opening a browser.

- `agent-browser find-url <keywords> [--browser chrome|edge] [--profile X]
  [--limit N] [--json]` — local command, no daemon. All keywords must match a
  bookmark's name or url; results are most-recently-added first.
- Cross-platform Bookmarks JSON paths (macOS / Linux / Windows), zero new deps
  (serde_json). Skips javascript:/data: bookmarklets.
- Skill docs: "pick the cheapest tool" matrix now points at find-url, plus a
  commands.md section.

Bookmarks only for now — visited-history is a locked SQLite DB and would need a
SQLite dependency (deferred to avoid C-dep cross-compile risk in the release
pipeline).

skill-data/core/SKILL.md

@@ -39,7 +39,7 @@ need a **real, logged-in browser** — not for reading text off a public page.
 | Discover what exists / find sources | `WebSearch` |
 | Specific facts from a static or public page | `WebFetch` or `curl` (no browser) |
 | Login state, interaction, JS-rendered or anti-bot pages | **agent-browser** (this skill) |
-| A page the user visited before / an internal system | local bookmarks & history, then agent-browser |
+| A page the user saved before / an internal system | `agent-browser find-url <keywords>` (their bookmarks), then open it |
 
 Don't hand-build deep URLs with query params — links discovered by *interacting*
 with the site carry the right hidden context and dodge anti-bot checks; a