chore(ci): skip perf and commits gates on Renovate-authored PRs (#23)

## Summary
Renovate's dep-bump PRs run the full pipeline today (`check`, `scan`, `commits`, `perf`, `a11y`). Two of those gates have near-zero signal on a typical bump and dominate the wall-clock cost:

- **`perf`** — Lighthouse build + 3-iteration median across the critical-routes list. 3-5 min per PR for a metric that is essentially zero on a patch/minor dep bump (the SPA today serves the static placeholder; even with real routes a typical bump stays inside the median noise floor).
- **`commits`** — re-validates commit messages that Renovate generates from a Conventional-Commits-conformant template. Tautological.

Skip both when the PR author is the `apf-portal-bot` Gitea user. The `push` event on `main` still runs the full pipeline post-merge, so any regression caught by `perf` is detected seconds after merge — fast enough to revert.

Net result: Renovate PRs run `check + scan + a11y` only, ≈ 4-5 min faster per PR.

## ADR amendment

ADR-0017 is amended in the same change:
- "Where Lighthouse CI runs" table now distinguishes human PR / bot PR / push to main / scheduled / local.
- New "Pre-merge gating policy: human PRs vs bot PRs" subsection records the rationale and the human-takeover edge case.
- §Confirmation entry for `perf` is reworded to reflect the conditional gate.

## Test plan
- [ ] After merge, the next Renovate-triggered PR (auto-rebase or new bump) shows only `check`, `scan`, `a11y` queued — no `perf`, no `commits`.
- [ ] A human-opened PR (e.g. this one) still queues all 5 gates.
- [ ] On `push` to `main` post-merge, the full pipeline runs including `perf`.

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Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #23

docs/development.md

@@ -244,7 +244,8 @@ Repo → Actions → "Renovate" workflow → Run workflow. Useful when you've ju
 
 ### Reviewing Renovate PRs
 
-- Each Renovate PR is gated by the same CI as a human PR — `check`, `scan`, `commits`, `perf`, `a11y`. Don't merge until all are green.
+- Renovate PRs run a leaner CI pipeline than human PRs — `check`, `scan`, `a11y` only. The `perf` and `commits` gates are skipped (per [ADR-0017](decisions/0017-performance-budgets-lighthouse-ci.md) — Lighthouse signal on a dep bump is essentially zero, commitlint on bot-generated messages is tautological). The full `perf` gate still runs on `push` to `main` post-merge, so regressions are caught seconds after merge rather than before.
+- Don't merge until the remaining gates are green.
 - The "Renovate Dependency Dashboard" issue (auto-created on first run) lists every pending update grouped by status. Use it to triage which PRs to expedite.
 - For a major bump that introduces breaking changes, **don't reflexively merge**: read the changelog, then either accept the work or close the PR with a "rejected" label. Renovate respects that label and won't keep re-opening the same major.
 - **Adding or removing** a dependency belongs in a feature PR, not in Renovate's scope. Renovate only updates _versions_ of existing deps.