§22 S2: Catalog + propose scoped to the active collection

Catalog reads the /c/:collectionId/ segment via useCollectionId and fetches the
collection-scoped catalog, building entry/proposal links with the active
collection; the propose modal threads the active collection so a propose from a
named collection targets it.

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

frontend/src/components/ProposeModal.jsx

@@ -28,7 +28,7 @@ function slugify(title) {
     .replace(/^-+|-+$/g, '')
 }
 
-export default function ProposeModal({ viewer, onClose, onSubmitted, initialTitle = '', projectId }) {
+export default function ProposeModal({ viewer, onClose, onSubmitted, initialTitle = '', projectId, collectionId }) {
   // #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.
@@ -98,6 +98,7 @@ export default function ProposeModal({ viewer, onClose, onSubmitted, initialTitl
         pitch: pitch.trim(),
         tags,
         proposedUseCase: useCase.trim() || null,
+        collectionId,
       })
       // v0.15.0 — analytics: fire on the §9.1 propose-RFC submit.
       // Slug is a stable, low-cardinality identifier (kebab-case