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/review_classifier.rs

@@ -14,6 +14,8 @@
 //!
 //! The operator is the `Remote-User` header the gateway sets, as for
 //! `agent_input`; the classifier names them in its journal line.
+//!
+//! [`review`] runs the same rules on a review request and posts the result.
 
 use std::collections::{BTreeMap, HashMap, HashSet};
 use std::fmt::Write as _;
@@ -35,6 +37,8 @@ use utoipa::{IntoParams, ToSchema};
 use crate::forge::{self, DefaultBranchFiles, PullForReview};
 use crate::{AppState, error_problem};
 
+pub(crate) mod review;
+
 /// How long a finished run's result stays readable.
 pub(crate) const RESULT_TTL: Duration = Duration::from_hours(1);
 
@@ -707,6 +711,12 @@ pub(crate) mod tests {
         files: Vec<(&'static str, String)>,
     }
 
+    impl Fake {
+        pub(crate) fn new(reply: Reply, files: Vec<(&'static str, String)>) -> Self {
+            Self { reply, files }
+        }
+    }
+
     impl PullSource for Fake {
         async fn pull(
             &self,
@@ -1017,6 +1027,15 @@ pub(crate) mod tests {
         })
     }
 
+    /// A JSON rules file holding the one `datetime` classification.
+    pub(crate) fn rules_json() -> (&'static str, String) {
+        let [_, json] = RULES_PATHS;
+        (
+            json,
+            rules_value(&serde_json::json!([datetime()]), &[]).to_string(),
+        )
+    }
+
     /// `file` as both formats, each with its path.
     fn both_formats(file: &serde_json::Value) -> [(&'static str, String); 2] {
         let [yml, json] = RULES_PATHS;