docs: describe container node deployment and the update flow [SKIP TESTS]

AGENTS.md

@@ -9,7 +9,7 @@ Monitor is a self-hosted network path quality monitor. Backend coordinates Agent
 - Treat `main` as the stable release branch and `dev` as the integration branch. Keep ordinary implementation work on `dev` or a feature branch; integrate into `main` through a pull request.
 - A push to `main` builds images only if its commit message contains `[CI]` (for a merged PR, put it in the PR or merge commit title). Without `[CI]` nothing is built; use `[CI SKIP]` to skip the pipeline entirely. When squashing or pushing to `main`, add `[CI]` unless a build is explicitly not wanted.
 - Before editing, inspect `git status`. Preserve pre-existing user changes: do not reset, clean, stash, or include unrelated files in a commit.
-- Do not commit credentials, API keys, registry passwords, or generated runtime data. CI credentials belong in Woodpecker secrets.
+- Do not commit credentials, API keys, registry passwords, or generated runtime data. CI credentials belong in Woodpecker secrets (`zot_secret`, `gitea_token`, `release_signing_key` for signing release manifests, `release_api_token` with the `release` scope). The release signing private key never goes into the repository or the panel; only the public key in `packaging/update/` does.
 - Keep development OCI images in the `monitor-dev/` repository path and release images in `monitor/`. Do not let a development build overwrite release tags such as `latest`.
 
 ## Project layout