§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/App.jsx

@@ -66,6 +66,10 @@ export default function App() {
   // right project. Falls back to the deployment default off a project route.
   const _projMatch = location.pathname.match(/^\/p\/([^/]+)/)
   const currentProjectId = (_projMatch && _projMatch[1]) || deployment.defaultProjectId
+  // §22 S2 — the collection the viewer is currently in (from the /c/<cid>/ URL
+  // segment), so a propose targets that collection. Falls back to the default.
+  const _colMatch = location.pathname.match(/^\/p\/[^/]+\/c\/([^/]+)/)
+  const currentCollectionId = (_colMatch && _colMatch[1]) || DEFAULT_COLLECTION
   // #28 Parts 2–3: the LinkedText create/contribute affordances route via
   // query params so they need no prop-threading from deep in a comment
   // list. `?propose=<term>` opens the propose modal pre-filled;
@@ -389,12 +393,13 @@ export default function App() {
           viewer={viewer}
           initialTitle={proposeParam || ''}
           projectId={currentProjectId}
+          collectionId={currentCollectionId}
           onClose={() => { setProposeOpen(false); clearParams('propose') }}
           onSubmitted={({ pr_number }) => {
             setProposeOpen(false)
             clearParams('propose')
             setCatalogVersion(v => v + 1)
-            navigate(proposalPath(currentProjectId, pr_number))
+            navigate(proposalPath(currentProjectId, pr_number, currentCollectionId))
           }}
         />
       )}