§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- tests updated to the three-tier schema; test_migration_028 retired (superseded by 029)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/tests/test_project_scoped_serving.py

@@ -11,18 +11,25 @@ from test_propose_vertical import (  # noqa: F401
 
 
 def _add_project(pid, name, vis="public"):
+    # §22 three-tier: a project + its default collection (keyed by the project
+    # id in tests, so default_collection_id(pid) == pid).
     from app import db
     db.conn().execute(
-        "INSERT OR IGNORE INTO projects (id, name, type, content_repo, visibility, initial_state) "
-        "VALUES (?, ?, 'document', ?, ?, 'super-draft')",
+        "INSERT OR IGNORE INTO projects (id, name, content_repo, visibility) VALUES (?, ?, ?, ?)",
         (pid, name, pid + "-content", vis),
     )
+    db.conn().execute(
+        "INSERT OR IGNORE INTO collections (id, project_id, type, subfolder, initial_state, visibility, name) "
+        "VALUES (?, ?, 'document', '', 'super-draft', ?, ?)",
+        (pid, pid, vis, name),
+    )
 
 
 def _add_rfc(slug, title, pid, state="active"):
     from app import db
+    # entries key by the project's default collection (id == pid in these tests)
     db.conn().execute(
-        "INSERT INTO cached_rfcs (slug, title, state, project_id) VALUES (?, ?, ?, ?)",
+        "INSERT INTO cached_rfcs (slug, title, state, collection_id) VALUES (?, ?, ?, ?)",
         (slug, title, state, pid),
     )