swarm-controller: harden the review classifier's real reviews

Follow-ups from the review of #5142.

A `Done` answer with fewer or more rows than the classifications sent, or
none, now posts the no-verdict comment instead of the classifier's overall
verdict, so a short answer can't approve.

Requests are accepted per repo, PR and head into a set bounded at the two
running plus eight waiting. A request for a key already running or waiting
starts nothing and logs at info; a request with every place taken starts no
run and posts a no-verdict comment saying so. Before, every delivery spawned
a task waiting on the semaphore, so toggling the review request queued one
paid run per toggle.

Table cells get a zero-width space after `#`, `!`, `://` and `www.`, so a
model's reason can't render an issue or PR reference or a bare URL as a link.

The secret publisher's policy denies the classifier's forge token leaf, the
way #5139 denied Grafana's admin password, with a module-eval-bao-grants arm
pinning it. The controller posts reviews with whatever token is there, so a
publisher write picked the account reviews come from.

Closes #5143, part of #5096.

swarm-controller/src/github_account.rs

@@ -135,7 +135,7 @@ mod tests {
             create_gate: std::sync::Arc::default(),
             accounts: Accounts::Fake(Arc::clone(store)),
             try_outs: super::super::review_classifier::TryOuts::default(),
-            review_slots: super::super::review_slots(),
+            reviews: std::sync::Arc::default(),
         }
     }