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-queue-client/src/review_classifier.rs

@@ -1,5 +1,6 @@
-//! The review classifier's try-out: the subject swarm-controller sends a run
-//! on, and what travels each way.
+//! The review classifier's runs: the subject swarm-controller sends a run
+//! on, and what travels each way. A try-out and a requested review are the
+//! same request.
 //!
 //! Three crates name these: the controller sends the request, the classifier
 //! answers it, and the auth-callout responder grants the one subject to each.
@@ -8,7 +9,7 @@ use std::time::Duration;
 
 use serde::{Deserialize, Serialize};
 
-/// The subject a try-out request goes to. The controller is its one
+/// The subject every run goes to. The controller is its one
 /// publisher and the classifier its one subscriber; the classifier answers
 /// on the request's reply subject.
 pub const SUBJECT: &str = "$SWARM.review-classifier.try-out";
@@ -34,7 +35,8 @@ pub const RUN_DEADLINE: Duration = Duration::from_mins(31);
 /// answer about it.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct TryOut {
-    /// The swarm UI user who started the run, as the gateway named them.
+    /// Who started the run: the swarm UI user, as the gateway named them, or
+    /// the forge user who requested the classifier's review.
     pub operator: String,
     /// `owner/name`.
     pub repo: String,