docs(roadmap): add markdown linting to Phase 15 scope

.planning/ROADMAP.md

@@ -3,7 +3,7 @@
 ## Milestones
 
 - ✅ **v1.0 MVP** — Phases 1–6 (shipped 2026-06-10) — see [`milestones/v1.0-ROADMAP.md`](milestones/v1.0-ROADMAP.md)
-- 🚧 **v1.1 Operability & Polish** — Phases 7–15 (planning) — mobile test harness, Gitea CI (runs the harness), faster write-back, in-app admin, per-event reminders, guided setup, real lint gate, desktop e2e, doc-only CI skip
+- 🚧 **v1.1 Operability & Polish** — Phases 7–15 (planning) — mobile test harness, Gitea CI (runs the harness), faster write-back, in-app admin, per-event reminders, guided setup, real lint gate, desktop e2e, doc-only CI skip + markdown lint
 
 ## Phases
 
@@ -33,7 +33,7 @@ Make FamilySync configurable, administrable, and maintainable for real multi-mem
 - [ ] **Phase 12: Initial Setup Wizard** - First-run validated bootstrap of env/VAPID/DB/OIDC + first app password, reusing the admin route surface
 - [x] **Phase 13: Real Lint Gate (ESLint)** - Wire ESLint flat config (typescript-eslint + React) across both apps so the Phase 8 CI lint slot actually fails on violations instead of no-op'ing (completed 2026-06-12)
 - [x] **Phase 14: Desktop E2E Coverage** - Add a Desktop Chrome Playwright profile + make the mobile-authored specs desktop-safe so the Phase 8 regression gate validates desktop, not just mobile (completed 2026-06-12)
-- [ ] **Phase 15: Doc-Only CI Skip** - Aggregate-gate the slow api/harness CI jobs so doc-only PRs to main merge without running them, without deadlocking branch protection (promoted from backlog 999.17)
+- [ ] **Phase 15: Doc-Only CI Skip + Markdown Lint** - Aggregate-gate the slow api/harness CI jobs so doc-only PRs to main merge without running them (no branch-protection deadlock), and add markdownlint to `fast-checks` so docs get a fast format+lint gate (promoted from backlog 999.17)
 
 ## Phase Details
 
@@ -262,20 +262,23 @@ Plans:
 
 ### Phase 15: Doc-Only CI Skip
 
-**Goal**: Doc-only PRs to `main` merge without running the slow `harness` (Playwright e2e + dev-stack bring-up, ~5 min) and `api` (MariaDB integration) jobs, while `fast-checks` (Prettier `format:check` covers markdown) still runs — and branch protection never deadlocks on a required check that never reports.
+**Goal**: Doc-only PRs to `main` merge without running the slow `harness` (Playwright e2e + dev-stack bring-up, ~5 min) and `api` (MariaDB integration) jobs, while `fast-checks` (Prettier `format:check` + markdown linting) still runs — and branch protection never deadlocks on a required check that never reports. Docs get a *fast but real* gate: format + lint, none of the slow code jobs.
 **Mode:** standard
-**Depends on**: Phase 8 (the `.gitea/workflows/ci.yml` it modifies) and Phase 13 (the `format:check` step that must keep running on docs). Independent of Phases 9–12.
+**Depends on**: Phase 8 (the `.gitea/workflows/ci.yml` it modifies) and Phase 13 (the `fast-checks` job + `format:check` step this extends). Independent of Phases 9–12.
 **Requirements**: TBD (promoted from backlog 999.17)
 **Success Criteria** (what must be TRUE):
 
   1. A doc-only PR to `main` (only `docs/` or `*.md` changed) skips the `api` and `harness` jobs but still runs `fast-checks`.
   2. A PR touching code runs `fast-checks`, `api`, and `harness` as today; a failure in any blocks the merge.
   3. Branch protection requires `CI / fast-checks` + an always-running `CI / gate` aggregate (passes when each heavy job is `success` OR `skipped`) — the direct `api`/`harness` requirements are dropped so a skipped heavy job never deadlocks the merge.
+  4. `fast-checks` runs a markdown linter (markdownlint-cli2) over `**/*.md`; an introduced markdown-lint violation fails the gate, and the existing markdown baseline passes (violations fixed or rules configured) so the gate starts green.
 
 **Pitfalls this phase owns**:
 
   - **Required-check deadlock** — never path-filter a required context directly; a required job that never reports blocks the PR forever. The always-running `gate` job (`if: always()`, passes on `success`/`skipped`) is the only safe gating surface.
   - **Gitea skipped-status quirk** — Gitea may not emit a commit-status for a `skipped` job; rely on the always-running `gate`, not on marking `api`/`harness` skipped-but-required.
+  - **Prettier vs markdownlint overlap** — Prettier already owns markdown *formatting*; scope markdownlint to *content* rules (heading increments, no broken/duplicate link refs, list/code-fence conventions) and disable its purely-stylistic rules that fight Prettier (e.g. line-length, list-indent), so the two don't conflict on the same `.md`.
+  - **`.planning/*` is push-direct, never linted** — planning bookkeeping bypasses CI via the Unprotected file pattern, so markdownlint never sees it; scope the lint glob to `docs/` + repo-root/app `*.md` and exclude `.planning/**` (and any generated markdown) to avoid a baseline cleanup of churny bookkeeping files.
 
 **Plans**: TBD
 **UI hint**: no
@@ -298,7 +301,7 @@ Plans:
 | 12. Initial Setup Wizard         | v1.1 | 0/?   | Not started | -       |
 | 13. Real Lint Gate (ESLint)      | v1.1 | 3/3   | Complete    | 2026-06-12 |
 | 14. Desktop E2E Coverage         | v1.1 | 1/1 | Complete    | 2026-06-12 |
-| 15. Doc-Only CI Skip             | v1.1 | 0/?   | Not started | -       |
+| 15. Doc-Only CI Skip + MD Lint   | v1.1 | 0/?   | Not started | -       |
 
 ## Backlog