build(docker): keep keys out of the image and run as non-root by default

The build context excluded only .env, so .env.local and the like or
pinokio/ENVIRONMENT would be baked into image layers; exclude every dotenv
file except .env.example, plus local state and QA output. Pin the base to
CI's Node 24.14.0 by digest, default to the image's node user, and correct
the HOST comment. Log the trusted peers as the operator's when set. README
notes that MCP and ChatGPT sign-in voice are unavailable under Docker, and
how to trust no gateway when widening the publish.

CHANGELOG.md

@@ -235,9 +235,10 @@
   [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`,
+- **Docker install path.** `docker compose up` builds on CI's Node 24.14.0 image,
+  pinned by digest, 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
+  (never root), so `.env`,
   `.gev-cache`, and `.gev-logs` persist on the host exactly as they do under
   `npm run dev` — Provider Settings included. The launcher
   (`scripts/docker-start.mjs`) trusts the container's gateway address for that