- New developer-guide/browser-provider-plugin.md: BrowserProvider ABC
(session lifecycle, CDP contract, bb_session_id back-compat key,
raise/never-raise split between create and close/cleanup),
get_setup_schema() hermes-tools integration, discovery, checklist.
Closes the one gap in the provider-plugin family — the ABC and
ctx.register_browser_provider() existed with zero docs.
- Register the page in the Plugins sidebar subcategory.
- Extend the routing map on the Plugins landing page (both locales)
with the previously missing rows: web-search, browser, secret-source,
and dashboard-auth surfaces.
