renovate: align the config with cluster-config

The shared jlab-renovate-bot instance serves this repo and cluster-config,
and two repos behaving differently under one bot is a source of surprises
rather than of safety. This adopts cluster-config's configuration:
config:best-practices in extends, labels ["renovate"], no PR caps
(prHourlyLimit 0, prConcurrentLimit 100), separateMinorPatch, an explicit
dependencyDashboard, and global automerge with platformAutomerge.

Two of those choices were previously wrong here and are now right, because
the branch protection on main has caught up: a review requirement and
validate-charts as a required check are both active. platformAutomerge
therefore arms the PR on the forge and Gitea merges it when the check
passes AND the review exists - the review is the gate, which is what makes
automerging majors something other than unattended merging.

Comments that asserted the opposite are rewritten rather than left to rot:
the platformAutomerge: false comment ("not (yet) a required check on either
side"), the "Majors stay manual" rule, the README PR policy bullets and the
required-check paragraph, and the CLAUDE.md forge notes.

config:best-practices pulls in docker:pinDigests, which is switched off
again for custom.regex and helm-values: an appVersion: is a tag by
construction and has nowhere to put a digest. Kept deliberately:
minimumReleaseAge of three days on the routine updates (every merge here
publishes a chart), the ignorePaths and ci/** opt-outs, every per-chart
manager, the nginx and qbittorrent constraints, and postUpgradeTasks.

Fixes #34

CLAUDE.md

@@ -54,8 +54,8 @@ Everything runs on the Gitea instance JLab-Git: issues, pull requests, CI and Re
 - **`tea`, not `gh`.** Work happens in a **Coder workspace, and it has no `op`** — that is the normal case here, not a broken environment, so do not wait for the 1Password CLI or propose installing it. Call `tea` directly; it carries the workspace's stored login and opens PRs and issues under the **bot account**, which is accepted. Say so in the report when something is authored that way. (`op plugin run -- tea`, the older instruction, applies only where `op` actually exists.)
 - **Remotes are named `github` and `JLab-Git`** — there is no `origin`. `JLab-Git/main` is the leading copy; say which remote you mean, because `git push` without one is ambiguous here.
 - **Branch protection with a signature requirement is active**, and signatures verify on Gitea. A commit that is not signed does not reach `main` — check before opening a PR, do not discover it at merge time.
-- **No merge queue.** Gitea has none, and its place is taken by **auto-merge on green checks**: the PR is armed once and merges itself when the required checks pass. Rule 6 above is unchanged — the user merges, and an agent never merges its own PR or arms auto-merge on it.
-- **A required check per chart is not possible.** Gitea runs a whole matrix as one job under one status context, so the install-test reports once for all charts. Relevant whenever branch protection is touched.
+- **No merge queue.** Gitea has none, and its place is taken by **auto-merge on green checks**: the PR is armed once and merges itself when the required check passes **and the required review exists** — both are active on `main`, so an armed PR without a review sits there instead of merging. Rule 6 above is unchanged — the user merges, and an agent never merges its own PR or arms auto-merge on it.
+- **A required check per chart is not possible.** Gitea runs a whole matrix as one job under one status context, so the install-test reports once for all charts. What is required on `main` is `validate-charts`, as that single context; per chart is the part that cannot be had. Relevant whenever branch protection is touched.
 - **Issue numbers changed with the move, and `#n` in this repo's files means the GitHub tracker.** The issues open at the time are Gitea #5–#21 and #24; the mapping is a comment on Gitea #14. Closed ones were not migrated and exist only on GitHub. Beware that Gitea silently resolves a bare `#n` against its own counter, so an old reference can render as a link to something unrelated. When you write a *new* reference, use the Gitea number.
 - **Renovate runs outside this repo**, as the shared `jlab-renovate-bot` instance; it reads our `renovate.json5` and its `postUpgradeTasks` hook is allow-listed there. **Do not add a Renovate workflow here** — a second runner means duplicate PRs and two schedulers rewriting each other's branches. README, "Renovate on Gitea", has the evidence.