feat(registry): hard-cut META_REPO -> REGISTRY_REPO; wire mirror into startup/webhook/sweep

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/hygiene.py

@@ -30,7 +30,7 @@ import logging
 import os
 from datetime import datetime, timedelta, timezone
 
-from . import db
+from . import db, projects as projects_mod
 from .bot import Bot
 from .config import Config
 
@@ -299,7 +299,7 @@ async def _delete_branch_via_bot(
         log.warning("hygiene: cannot delete %s/%s — slug missing from cache", slug, branch)
         return False
     if not rfc["repo"]:
-        owner, repo = config.gitea_org, config.meta_repo
+        owner, repo = config.gitea_org, (projects_mod.default_content_repo(config) or "")
     elif "/" in rfc["repo"]:
         owner, repo = rfc["repo"].split("/", 1)
     else: