swarm-controller: post the review classifier's verdict on a review request

Requesting the forge account `review-classifier` as a reviewer now runs the
repo's rules against the PR and posts the result as that account's review,
on the head commit the run read. A push starts no run; only a fresh review
request does.

- An instance-wide `pull_request_review_request` system hook delivers to
  `/webhook/forge/review-request`. A request for any other reviewer, or a
  removed request, does nothing.
- The controller reads the PR, loads the rules with the same reader as
  `GET /api/review-classifier/rules`, sends one request on the try-out
  subject, and posts APPROVED or REQUEST_CHANGES with the table as the body.
- With no clean verdict (PR or rules don't load, the run fails, or any
  classification has no answer) it posts a COMMENT saying why, never an
  approval. The event is one function, `no_clean_verdict_event`.
- Table cells are flattened, markup-escaped, and every `@` gets a
  zero-width space, so a model's reason can't break the table or mention
  anyone.
- At most two requested reviews run at once; the rest wait in memory.
- The account is minted the way hive accounts are: a five-minute pass
  queues a `MintClassifierForgeToken` node when the token at
  `swarm/services/review-classifier/forge/token` is missing or stale. The
  token is `write:repository`. The controller's bao policy gains that leaf
  (create/read/update), pinned in module-eval bao-grants. The classifier
  never sees the token.

The account gets no repo access automatically; a repo admin adds it by
hand. A re-request retires the account's earlier review: Forgejo clears
`official` on a reviewer's earlier reviews when it is requested again
(models/issues/review.go AddReviewRequest, v16.0.5), and approvals and
rejection blocks count official reviews only.

Refs #5137

swarm-controller/src/forge.rs

@@ -40,6 +40,7 @@ use crate::webhook::DeliveryKind;
 use swarm_queue_client::review_classifier::Commit;
 
 pub mod agent_token;
+pub mod classifier_account;
 pub mod docs_grant;
 pub mod hive_token;
 pub mod legacy_tokens;
@@ -1289,6 +1290,9 @@ impl Client {
                 // in an org created after this hook was registered, with no
                 // per-org registration to keep in sync as orgs come and go.
                 DeliveryKind::VcsActivity => ("push", HookScope::Instance),
+                // Instance-wide too: any repo whose admin gave the
+                // classifier's account access can request its review.
+                DeliveryKind::ReviewRequest => ("pull_request_review_request", HookScope::Instance),
             };
             self.ensure_hook(&scope, &target_url, event, secret)
                 .await