docs(15): create phase plan — doc-only CI skip + markdown lint

3 plans across 3 waves:
- 15-01: markdownlint-cli2 config/script/step + fix 13 baseline violations (SC-4)
- 15-02: ci.yml changes job + conditional api/harness + always-running gate (SC-1/2, SC-3 YAML)
- 15-03: operator branch-protection checkpoint + publish.yml comment (SC-3)

.planning/ROADMAP.md

@@ -280,7 +280,14 @@ Plans:
   - **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
+**Plans**: 3 plans (3 waves)
+
+Plans:
+
+- [ ] 15-01-PLAN.md — markdownlint-cli2 + `.markdownlint-cli2.jsonc` + `md:lint` script + fast-checks step + fix 13 baseline violations (SC-4)
+- [ ] 15-02-PLAN.md — ci.yml: `changes` (dorny/paths-filter@v4) + conditional api/harness + always-running `gate` aggregate (SC-1/SC-2, SC-3 YAML)
+- [ ] 15-03-PLAN.md — operator branch-protection checkpoint (require `CI / fast-checks` + `CI / gate`, drop api/harness) + publish.yml comment update (SC-3)
+
 **UI hint**: no
 
 ## Progress
@@ -301,7 +308,7 @@ 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 + MD Lint   | v1.1 | 0/?   | Not started | -       |
+| 15. Doc-Only CI Skip + MD Lint   | v1.1 | 0/3   | Planned     | -       |
 
 ## Backlog