review classifier: commit shas and index lines stay out of the prompt

Every classification's shared context began with the PR's head sha,
headed each commit with its sha, and carried each file's
`index <hash>..<hash>` line in the diff. A push or rebase rewrites all
of those, so the provider's prompt cache missed from the first line of
the user message even when the commit messages and hunks were
unchanged (#5245: "cache hits show as 0.1x").

The header now names only repo#pr, each commit is headed by its
position, and the diff drops `index` lines before lockfiles collapse.
The `diff --git` paths and every hunk stay. The TryOut's head_sha is
untouched: the controller still posts the review against it, and the
journal line still logs it.

On the ACP runtime the cost sink also adds each classification's tokens
to `hyperhive.review_classifier.token.usage`, typed input / output /
cacheRead / cacheCreation like claude's own `claude_code.token.usage`,
so the hit rate is a number in the metrics store on both runtimes.

swarm-review-classifier/src/acp.rs

@@ -175,6 +175,7 @@ impl<S: CostSink> Acp<S> {
             pr: run.pr,
             model: provider.model.clone(),
             amount: crate::cost::amount(&provider.prices, usage),
+            usage: *usage,
         });
     }
 }
@@ -387,6 +388,10 @@ done
             ("o/r", 7, "qwen")
         );
         assert!((cost.amount - 0.006).abs() < 1e-12, "{}", cost.amount);
+        assert_eq!(
+            (cost.usage.input_tokens, cost.usage.output_tokens),
+            (1000, 200)
+        );
     }
 
     #[tokio::test]