§22 S1: thread collection_id through backend + update tests (N=1 unchanged, 454 green)

- collections.py resolution helpers (default_collection_id, type, initial_state)
- registry mirror writes project grouping fields + default-collection corpus fields
- auth.project_of_rfc joins collections; project_member_role reads memberships
- cache/api_*/funder writers+readers re-keyed to collection_id (cached_prs + denormalised
  project_id tags unchanged); api_deployment reads type/initial_state from the default collection
- projects.py restamp detects bootstrap via collections; initial_state via collection
- tests updated to the three-tier schema; test_migration_028 retired (superseded by 029)
- add @S1 acceptance test (collection grain + N=1 serving)

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

backend/app/api_graduation.py

@@ -574,7 +574,7 @@ def make_router(
     # -------------------------------------------------------------------
 
     def _require_super_draft(slug: str, viewer):
-        row = db.conn().execute("SELECT * FROM cached_rfcs WHERE slug = ?", (slug,)).fetchone()
+        row = db.conn().execute("SELECT *, (SELECT c.project_id FROM collections c WHERE c.id = cached_rfcs.collection_id) AS project_id FROM cached_rfcs WHERE slug = ?", (slug,)).fetchone()
         if row is None:
             raise HTTPException(404, "RFC not found")
         # §22.5 visibility gate (subtractive, §22.7): gated → 404 to non-members.
@@ -584,7 +584,7 @@ def make_router(
         return row
 
     def _require_retirable(slug: str):
-        row = db.conn().execute("SELECT * FROM cached_rfcs WHERE slug = ?", (slug,)).fetchone()
+        row = db.conn().execute("SELECT *, (SELECT c.project_id FROM collections c WHERE c.id = cached_rfcs.collection_id) AS project_id FROM cached_rfcs WHERE slug = ?", (slug,)).fetchone()
         if row is None:
             raise HTTPException(404, "RFC not found")
         if row["state"] not in ("super-draft", "active"):
@@ -592,7 +592,7 @@ def make_router(
         return row
 
     def _require_retired(slug: str):
-        row = db.conn().execute("SELECT * FROM cached_rfcs WHERE slug = ?", (slug,)).fetchone()
+        row = db.conn().execute("SELECT *, (SELECT c.project_id FROM collections c WHERE c.id = cached_rfcs.collection_id) AS project_id FROM cached_rfcs WHERE slug = ?", (slug,)).fetchone()
         if row is None:
             raise HTTPException(404, "RFC not found")
         if row["state"] != "retired":