Review fixes: trailing-slash URLs, pack refetch on server change, ru autofill ...

Findings from the full extension review (0.2.4):
- api.js built "baseUrl/api/v1/..." without stripping a trailing slash —
  "//api/v1/secrets" requests on a base URL saved with one; now stripped
  at the single URL-building point (same trap as the webhook 405).
-SAVE_SETTINGS now triggers a design-pack refetch: the install-time fetch
  runs against the DEFAULT baseUrl, so a user pointing the extension at
  another server would not see that server's pack until browser restart.
- The autofill card failed to fill fields named in russian (логин/почта)
  — username-name matching now covers them (password side already did).
- activeTab removed (never used); manifest description is now
  user-facing. Version 0.2.4, fresh dist zips and release manifest.

Co-Authored-By: Claude Code <noreply@anthropic.com>

Revoked tokens stop being invisible: popup plate + token ID, tokens table columns ...

Extension 0.2.2: a 401 from any API call flips a tokenInvalid flag that the
popup renders as a dedicated plate (same load, via status propagation from
the background, plus the pre-flagged check on popup open); the Settings
drawer shows the stored token's public ID so it can be matched against the
tokens table. Web: Tokens tab gains Public ID / Created / Last used columns.
Design pack v24 ships the new strings (en/uk/ru); served zips rehashed.

Co-Authored-By: Claude Code <noreply@anthropic.com>

Import browser extension source under extensions/extension ...

Move the gnexus-creds-extension sources (Chrome/Firefox MV3) from the
separate sibling repository into extensions/extension/ so builds live
next to the packaged releases this service distributes
 (extensions/dist/ + extensions/manifest.json, untouched).

- add a reproducible `make lib` target materializing lib/ from the
  frontend's pinned gnexus-ui-kit (gitignored, like before)
- drop the playwright-only package.json/lock; system node+zip suffice
- scoped .gitignore so it cannot shadow tracked extensions/dist zips
- README (main + extension): document the in-repo build and publish flow

Rebuilt zips differ from released ones only in the three lib files
(older kit in the release); extension code itself is byte-identical.

Co-Authored-By: Claude Code <noreply@anthropic.com>