auditor: fix two false-positive classes from cloud inference

Observed on PR #8 audit (de11ac4): 7 warn findings, all from the
cloud inference check. Investigation showed two distinct bug classes
that weren't "ship bad code", they were "auditor misreads the diff":

1. Cloud flagged "X not defined in this diff / missing implementation"
   for symbols like `tailJsonl` and `stubFinding` that ARE defined —
   just not in the added lines of this diff. Fix: extract candidate
   symbols from the cloud's gap summary, grep the repo for their
   definitions (function/const/let/def/class/struct/enum/trait/fn).
   If every named symbol resolves, drop the finding; if some do,
   demote to info with the resolution in evidence.

2. Cloud flagged runtime metrics like "58 cloud calls, 306s
   end-to-end" as unbacked claims. These are empirical outputs
   from running the test, not things a static diff can prove.
   Fix: claim_parser now has an `empirical` strength class
   matching iteration counts, cloud-call counts, duration metrics,
   attempt counts, tier-count phrases. Inference drops empirical
   claims from its cloud prompt (verifiable[] subset only) and
   claim-index mapping uses verifiable[] so cloud responses still
   line up.

Added `claims_empirical` to audit metrics so the verdict is
introspectable: how many claims WERE runtime-only vs how many
are diff-verifiable?

Verified: unit tests confirm empirical classification on 5
sample commit messages; symbol resolver found both false-positive
symbols (tailJsonl + stubFinding) and correctly skipped a known-
fake symbol.

auditor/audit.ts

@@ -77,6 +77,7 @@ export async function auditPr(pr: PrSnapshot, opts: AuditOptions = {}): Promise<
     claims_strong: claims.filter(c => c.strength === "strong").length,
     claims_moderate: claims.filter(c => c.strength === "moderate").length,
     claims_weak: claims.filter(c => c.strength === "weak").length,
+    claims_empirical: claims.filter(c => c.strength === "empirical").length,
     claims_total: claims.length,
     diff_bytes: diff.length,
   };