feat: add a Docker install path

Vite's dev server is the whole app here — it serves the client and runs every
API proxy as middleware — so one container running `npm run dev` covers it, and
HOST/PORT are already env-driven.

Three details are deliberate:

- The port publishes to 127.0.0.1. Docker's usual "4173:4173" binds every host
  interface, which would silently make the README's LAN warning the default for
  a server that brokers configured provider keys.
- The repo is bind-mounted, so keys saved from Provider Settings, .gev-cache
  and .gev-logs persist on the host exactly as they do under `npm run dev`.
  node_modules stays in the image so a host install cannot shadow the
  Linux-built native deps.
- The container runs as the host user, since everything it writes lands in
  that bind mount. Vite's dep optimizer still needs to write inside the image's
  node_modules, hence the two loosened directories.

Puppeteer's Chromium download is skipped: it is only needed by `npm run
test:track`, which the README points at the host.

Co-Authored-By: Claude Opus 5 <[email protected]>

CHANGELOG.md

@@ -107,6 +107,12 @@
   [TheSmokeDev](https://github.com/TheSmokeDev) for the credential handling
   from #653.
 
+- **Docker install path.** `docker compose up` builds the pinned Node image and
+  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`.
+
 - 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
   now select one winner; unavailable storage or a busy repair retains the