fix(models): treat subscription session/usage-limit stdout as exhaustion

Subscription CLIs (claude) report a hit session limit as ordinary stdout with a
ZERO exit code — 'You've hit your session limit · resets …'. Left as Ok it
became a 'response' each agent then failed to parse, and the run burned every
remaining agent against a dead session instead of pausing. Now the sentinel is
caught (length-guarded so a real finding mentioning 'rate limit' is not misread)
and surfaced as exhaustion, so the pool parks the run for /continue — the
pause-on-quota path that already existed but this case never reached.

Found during a live benchmark when run B collapsed to 0 findings mid-run.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

neurosploit-rs/crates/harness/src/pool.rs

@@ -15,6 +15,7 @@ pub fn is_exhaustion(e: &anyhow::Error) -> bool {
         "quota", "insufficient_quota", "insufficient quota", "out of credit",
         "credit balance", "billing", "exhausted", "overloaded", "capacity",
         "usage limit", "resource_exhausted", "resource exhausted",
+        "session limit", "session/usage limit", "you've hit your",
     ]
     .iter()
     .any(|k| s.contains(k))