fix(apply): bound the blast-radius up-walk; fix two stale comments

Second-review follow-ups on the ownership cleanups:

- The new `group_blast_radius` `app_chain` recursion walked app→root with no
  depth cap, unlike the `ancestors()` CTE it replaced (`WHERE c.depth < 64`).
  Add the same `ac.depth < 64` guard so a (should-be-impossible) cycle in
  `groups.parent_id` can't spin the recursive CTE unbounded and hang a plan.
- Drop the now-false "memoized per group" line from `group_blast_radius`'s doc
  (it is a single set-based query now).
- Correct the `PlanRequest` flatten comment: apply is deliberately NOT flattened
  (its pre-§7 wire was already `{bundle, …}`), so the two endpoints are
  asymmetric by history — the old comment wrongly claimed parity.

Verified: the blast-radius journey + ownership journeys still pass; the INNER
JOIN to `projects` is safe (owner_project FK is ON DELETE SET NULL, so a
non-NULL owner always references a live row — no dangling drop).

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

crates/manager-core/src/apply_service.rs

@@ -2192,8 +2192,7 @@ impl ApplyService {
     /// §7 M3.2: descendant apps of `gid` grouped by their nearest-claimed-
     /// ancestor project, EXCLUDING `exclude` (the planning project) — the apps
     /// a change to `gid`'s inherited config fans out to across other repos.
-    /// Ancestor resolution is memoized per group, so the cost is one walk per
-    /// distinct descendant group, not per app.
+    /// Resolved in one set-based recursive query (see below).
     async fn group_blast_radius(
         &self,
         gid: GroupId,
@@ -2218,7 +2217,7 @@ impl ApplyService {
                UNION ALL
                  SELECT ac.app_id, g.parent_id, ac.depth + 1
                  FROM app_chain ac JOIN groups g ON g.id = ac.gid
-                 WHERE g.parent_id IS NOT NULL
+                 WHERE g.parent_id IS NOT NULL AND ac.depth < 64
              ),
              nearest AS (
                  SELECT DISTINCT ON (ac.app_id) ac.app_id, g.owner_project