fix(docker): let Provider Settings admit the host through the published port

Docker delivers the host's own browser to the container from the container
network's gateway, never from 127.0.0.1, so the loopback-only admission gate
answered every POWER UP request with 403 and no key could be saved. The README
and CHANGELOG claimed otherwise; both are corrected here.

- keySetupCore: GEV_KEY_SETUP_TRUSTED_PEERS, an exact-address list (no
  wildcards, prefixes or hostnames) admitted alongside loopback. Unset trusts
  nothing, and the sharing, Host, Origin, Content-Type and proxy-header checks
  all still apply to a listed address. Twelve assertions pin each refusal.
- scripts/docker-start.mjs: the container entry point, shaped after
  scripts/pinokio-start.mjs. It reads the default gateway from /proc/net/route,
  trusts exactly that address, and starts Vite. No gateway (--network none)
  trusts nothing. The pure helpers are unit-tested and a contract test pins the
  Dockerfile CMD and the loopback-only publish.
- Dockerfile: install git. `npm test` builds fixtures with `git init`, so the
  suite failed 71 tests inside the image and the README's claim that it runs in
  the container was wrong.
- SECURITY.md and .env.example document the setting and why it is safe only
  behind a 127.0.0.1 publish; README gains the Linux/NAS id note and .dockerignore
  drops macOS AppleDouble sidecars, both reported on the PR.

Verified in Docker on a clean build: saving a key from the panel writes the
bind-mounted .env (0600 in the container), it survives `compose down`/`up`, and
REMOVE comments it back out. A foreign Origin, a foreign Host, a proxy header
and a sibling container on the same network are each refused. `npm run doctor`,
`npm test` (5067 passed, 1 skipped, 0 failed) and `npm run build` are green
inside the container.

Reported-by: @jklaze
Co-Authored-By: Bogdan Petrut <[email protected]>
Co-Authored-By: Claude Opus 5 <[email protected]>

CHANGELOG.md

@@ -111,7 +111,15 @@
   serves the app on `http://localhost:4173` with no local Node install. The repo
   is bind-mounted and the container runs as the host user, so `.env`,
   `.gev-cache`, and `.gev-logs` persist on the host exactly as they do under
-  `npm run dev`.
+  `npm run dev` — Provider Settings included. The launcher
+  (`scripts/docker-start.mjs`) trusts the container's gateway address for that
+  panel, since that is where Docker delivers the host's own browser from; the
+  opt-in behind it, `GEV_KEY_SETUP_TRUSTED_PEERS`, takes exact addresses only
+  and is unset (so loopback-only, unchanged) under every other launcher.
+  Thanks to [jklaze](https://github.com/jklaze) for finding and diagnosing the
+  container-to-host 403, and to [14traits](https://github.com/14traits),
+  [PoBruno](https://github.com/PoBruno) and [milu70hub](https://github.com/milu70hub)
+  for testing on Apple silicon, Docker Engine on Linux, and NAS hosts.
 
 - Stdio servers from one install share a panel key so a page read from one
   process can make requests through another. Concurrent malformed-key repairs