v0.31.0: meta-only repository topology (ROADMAP #36)

Retire the per-RFC-repo model. RFCs now live in their meta-repo entry
(rfcs/<slug>.md) for their whole life; graduation is an in-place
super-draft → active state flip that keeps the body in the entry — no
repo creation, no body-strip, no five-step transaction, no rollback.

SPEC: §1 topology rewritten (one meta/content repository, no per-RFC
repos) with a deployer-facing "single content repository" framing; §2
(repo: always-null), §3 (active is in-place), §4, §9.8 (handoff
frictions dissolve), and §13 fully rewritten (two-field dialog, "The
flip", §13.6 RFC-0001 fold-back record).

Code: graduation collapses to open+merge one frontmatter PR; branch/PR/
chat dispatch re-keyed on meta-residency (repo IS NULL) so active RFCs
edit on the meta repo exactly as super-drafts do; the two "RFC has no
repo" 409 guards removed; promote-to-branch slug-embeds an active RFC's
auto-branch (edit-<slug>-<hex>) for shared-repo cache attribution;
refresh_meta_branches + hygiene branch-resolution include meta-resident
actives; the §9.8 read-only guard + pre_graduation_history scoped to
legacy per-repo only; dead bot primitives + GraduateDialog repo field +
blocking-PR popover removed. The repo: frontmatter field and the
/blocking-prs endpoint are retained (schema stability / informational).

Tests: graduation suite rewritten to the flip model; e2e + hygiene
updated. Full backend suite 375 passed; frontend builds.

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

backend/app/hygiene.py

@@ -284,9 +284,10 @@ async def _delete_branch_via_bot(
     reason: str,
 ) -> bool:
     """Call `bot.delete_branch` with the system actor. Resolves the
-    `(org, repo)` pair from the slug: super-draft edit branches and
-    graduation branches live on the meta repo; active-RFC branches
-    live on the per-RFC repo named by `cached_rfcs.repo`.
+    `(org, repo)` pair from the slug: under the meta-only topology (§1)
+    every meta-resident entry's edit branches and graduation branches
+    live on the meta repo; a legacy per-RFC repo (a `repo:` that survives
+    from before the fold-back, §13.6) is named by `cached_rfcs.repo`.
 
     Returns True on a clean delete; False if the rfc row is missing
     (we leave the branch row in place — a subsequent reconciler sweep
@@ -297,12 +298,13 @@ async def _delete_branch_via_bot(
     if rfc is None:
         log.warning("hygiene: cannot delete %s/%s — slug missing from cache", slug, branch)
         return False
-    if rfc["state"] == "super-draft":
+    if not rfc["repo"]:
         owner, repo = config.gitea_org, config.meta_repo
-    elif rfc["state"] == "active" and rfc["repo"] and "/" in rfc["repo"]:
+    elif "/" in rfc["repo"]:
         owner, repo = rfc["repo"].split("/", 1)
     else:
-        log.warning("hygiene: cannot resolve repo for %s state=%s", slug, rfc["state"])
+        log.warning("hygiene: cannot resolve repo for %s state=%s repo=%r",
+                    slug, rfc["state"], rfc["repo"])
         return False
     try:
         await bot.delete_branch(