§22 M3-backend Plan B (write path, propose): project-scoped propose (v0.38.0)

A new entry can be proposed into a specific project; it lands in that project's
content repo and shows under that project's proposals. A non-default project is
no longer read-only.

- api.py: POST /api/projects/{pid}/rfcs/propose (propose body extracted into a
  project-parameterized helper; unscoped /api/rfcs/propose kept as default
  compat). Slug uniqueness, idea-PR reservation, landing state, and the
  proposed_use_cases row scoped to the target project. GET
  /api/projects/{pid}/proposals.
- cache.py: refresh_meta_pulls loops every project's content_repo, stamping
  cached_prs.project_id; projects.content_repo(pid) helper.
- frontend: proposeRFC(projectId,…)/listProposals(projectId); ProposeModal
  takes projectId; App resolves current project from the /p/<id>/ URL; Catalog
  lists that project's proposals.
- tests: test_project_scoped_propose.py (lands scoped + gated 404). 447 backend
  + 11 Vitest green; clean build.

Known limitation: branch/PR/graduation edit flows + default-id re-stamp not yet
scoped (next slice). Per docs/superpowers/specs/2026-06-04-m3-backend-planb-design.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/Catalog.jsx

@@ -35,7 +35,7 @@ export default function Catalog({ viewer, onProposeRFC, version }) {
 
   useEffect(() => {
     listRFCs(pid).then(d => setRfcs(d.items)).catch(() => setRfcs([]))
-    listProposals().then(d => setProposals(d.items)).catch(() => setProposals([]))
+    listProposals(pid).then(d => setProposals(d.items)).catch(() => setProposals([]))
   }, [version, pid])
 
   const filtered = useMemo(() => {

frontend/src/components/ProposeModal.jsx

@@ -28,7 +28,7 @@ function slugify(title) {
     .replace(/^-+|-+$/g, '')
 }
 
-export default function ProposeModal({ viewer, onClose, onSubmitted, initialTitle = '' }) {
+export default function ProposeModal({ viewer, onClose, onSubmitted, initialTitle = '', projectId }) {
   // #28 Part 2: a "create RFC for '<term>'" affordance pre-fills the title
   // (App passes the `?propose=<term>` value here); the slug derives from it
   // via the same effect that drives manual typing.
@@ -92,7 +92,7 @@ export default function ProposeModal({ viewer, onClose, onSubmitted, initialTitl
     setSubmitting(true)
     setError(null)
     try {
-      const result = await proposeRFC({
+      const result = await proposeRFC(projectId, {
         title: title.trim(),
         slug,
         pitch: pitch.trim(),