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]>

.dockerignore

@@ -0,0 +1,6 @@
+node_modules
+.git
+.env
+.gev-cache
+.gev-logs
+dist