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.

README.md

@@ -171,8 +171,12 @@ Open **`http://localhost:4173`** as above. Everything the app saves stays in the
 
 Back up that folder and you've backed up everything; delete `.env` to forget your keys. Source edits still hot-reload. The port is published to `127.0.0.1` only, so the default matches the native one.
 
+The local MCP server and ChatGPT OAuth voice are not available under Docker; use an OpenAI API key for voice.
+
 Publishing it wider is the [Sharing an instance](#-sharing-an-instance) opt-in, and it hands out **Provider Settings** too: the launcher trusts the container gateway as this machine, and a wider publish delivers everyone else from that same address. For an instance you mean to share, put the keys in `.env` by hand instead. [SECURITY.md](SECURITY.md) has the detail.
 
+When you widen the publish, also set `GEV_KEY_SETUP_TRUSTED_PEERS=none` so the launcher trusts no gateway address.
+
 <details>
 <summary>Running on Linux, a NAS, or behind a reverse proxy</summary>