Release extension 0.1.1: kit 1.0 lib, shield logo icons ...

Rebuild both browsers' packages against gnexus-ui-kit 1.0 (make lib
from frontend/node_modules) and swap the generic dots mark for the
shield keyhole logo rasterized from frontend/public/logo.svg
(icon.svg + 16/32/48/128 PNG rsvg-convert). Popup verified in
chromium: settings drawer and secrets list render with no page errors.
Version bumped in extension manifest + Makefile; extensions/manifest.json
points at the 0.1.1 zips with fresh sha256/size (0.1.0 zips removed).

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>