§22 S2: collection-scoped frontend path + API helpers

useCollectionId() hook; listRFCs/getRFC/proposeRFC take an optional collection
id and target the /collections/<cid>/ routes; add listCollections +
createCollection.

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

frontend/src/api.collections.test.js

@@ -0,0 +1,48 @@
+// §22 S2 — the API client builds collection-scoped URLs when a collection id is
+// supplied, and falls back to the project/default-collection paths otherwise.
+import { describe, it, expect, vi, afterEach } from 'vitest'
+import { listRFCs, getRFC, proposeRFC, listCollections } from './api.js'
+
+function mockFetch() {
+  const fn = vi.fn(async () => ({
+    ok: true,
+    status: 200,
+    json: async () => ({ items: [] }),
+  }))
+  global.fetch = fn
+  return fn
+}
+
+afterEach(() => { vi.restoreAllMocks() })
+
+describe('collection-scoped api URLs', () => {
+  it('listRFCs scopes to a collection when given one', async () => {
+    const f = mockFetch()
+    await listRFCs('ohm', 'features')
+    expect(f).toHaveBeenCalledWith('/api/projects/ohm/collections/features/rfcs')
+  })
+
+  it('listRFCs falls back to the project default path without a collection', async () => {
+    const f = mockFetch()
+    await listRFCs('ohm')
+    expect(f).toHaveBeenCalledWith('/api/projects/ohm/rfcs')
+  })
+
+  it('getRFC scopes to a collection when given one', async () => {
+    const f = mockFetch()
+    await getRFC('ohm', 'login', 'features')
+    expect(f).toHaveBeenCalledWith('/api/projects/ohm/collections/features/rfcs/login')
+  })
+
+  it('proposeRFC targets the collection-scoped propose route', async () => {
+    const f = mockFetch()
+    await proposeRFC('ohm', { title: 'T', slug: 's', pitch: 'p', tags: [], collectionId: 'features' })
+    expect(f.mock.calls[0][0]).toBe('/api/projects/ohm/collections/features/rfcs/propose')
+  })
+
+  it('listCollections hits the project collections route', async () => {
+    const f = mockFetch()
+    await listCollections('ohm')
+    expect(f).toHaveBeenCalledWith('/api/projects/ohm/collections')
+  })
+})