§22 S2: create-collection endpoint (bot commit + registry refresh)

POST /api/projects/<id>/collections, owner/admin-gated, commits a
.collection.yaml to the content repo main via bot.create_collection, then
re-mirrors the registry so the collections row appears (§22.2). Adds GET
list/one collection routes. Extends FakeGitea to model directory listings so
the mirror's content-repo walk is exercised end to end.

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

backend/app/api.py

@@ -21,6 +21,7 @@ from pydantic import BaseModel, Field
 from . import (
     api_admin,
     api_branches,
+    api_collections,
     api_contributions,
     api_deployment,
     api_discussion,
@@ -152,6 +153,7 @@ def make_router(
     # §22.9/§22.10 (M3): runtime deployment + per-project config (replaces
     # VITE_APP_NAME) + the old-URL 308 redirects.
     router.include_router(api_deployment.make_router(config))
+    router.include_router(api_collections.make_router(config, gitea, bot))
 
     # ---------------------------------------------------------------
     # §17: /api/health — unauthenticated post-flight probe.