fix(§22/G-15): make the branch/edit/body subsystem three-tier aware (v0.53.0)

§22 migrated the READ/catalog path to the three-tier (project/collection)
model but the WRITE/branch/body subsystem still hardcoded the default
project's default collection — resolving every meta-resident entry to the
default content repo at rfcs/<slug>.md, ignoring the entry's project (its own
content repo) and collection (a <subfolder>/rfcs/ prefix). An entry outside
the default collection rendered a blank canonical body and every edit/PR/
body-write path hit the wrong file.

- New single resolver: projects.content_repo_for_collection() +
  projects.entry_location(config, cid, slug) -> (org, repo, md_path)
  (collection -> project -> content_repo + subfolder; falls back to the
  default repo for a legacy/unknown collection).
- Every entry write/read path resolves via it: api_branches (body GET + all
  branch write paths), api_prs (pr-draft/open/merge/withdraw/review/
  resolution-branch), api_graduation (graduate/claim/retire/unretire +
  orchestrator + state-flip), api.py mark-reviewed + idea-PR merge/decline/
  withdraw + proposal preview, api_metadata. bot.open_metadata_pr and
  bot.mark_entry_reviewed gained a file_path param. refresh_meta_branches,
  the webhook corpus-refresh dispatch, and the hygiene branch-delete now
  span every project's content repo, not just the default.
- New additive collection-scoped body-read routes:
  GET /api/projects/{pid}/collections/{cid}/rfcs/{slug}/main and
  .../branches/{branch} disambiguate a slug across collections (G-5) and read
  the entry's own repo. Slug-only routes kept (now collection-aware via the
  cached row). Frontend getRFCMain/getBranch take optional pid+cid; RFCView
  threads them (mirrors the v0.52.1 entry-detail fix).

No migration, no config change. Existing default-collection entries
unaffected. Tests: backend resolver + collection-scoped branch/body + graduate-
in-subfolder write path; frontend api unit. backend 677 / frontend 60 green.

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

backend/app/hygiene.py

@@ -293,20 +293,21 @@ async def _delete_branch_via_bot(
     (we leave the branch row in place — a subsequent reconciler sweep
     will reconcile or the operator can intervene)."""
     rfc = db.conn().execute(
-        "SELECT state, repo FROM cached_rfcs WHERE slug = ?", (slug,)
+        "SELECT state, repo, collection_id FROM cached_rfcs WHERE slug = ?", (slug,)
     ).fetchone()
     if rfc is None:
         log.warning("hygiene: cannot delete %s/%s — slug missing from cache", slug, branch)
         return False
     if not rfc["repo"]:
-        repo = projects_mod.default_content_repo(config)
+        # §22/G-15: the edit/graduation branch lives on the entry's COLLECTION's
+        # project content_repo, not the deployment default.
+        owner, repo, _ = projects_mod.entry_location(config, rfc["collection_id"], slug)
         if not repo:
             log.warning(
-                "hygiene: default project has no content_repo; skipping branch delete for %s/%s",
+                "hygiene: no content_repo resolved; skipping branch delete for %s/%s",
                 slug, branch,
             )
             return False
-        owner = config.gitea_org
     elif "/" in rfc["repo"]:
         owner, repo = rfc["repo"].split("/", 1)
     else: