v0.11.2 — Explain empty reviews

Patch: a zero-finding review now explains itself instead of rendering a bare "No findings.".

When the model returns no findings (a clean PR, an under-producing model, or findings that all fell outside the diff), the check-run summary now states why — distinguishing "no issues above your configured floors" from "N findings dropped as outside the diff", and pointing at confidence_floor / severity_floor when you expected more. Applied to both the single-call and chunked paths (the chunked path previously had no empty-review diagnostic, and the single-call path only spoke up for reasoning models).

This is legibility, not recall: it makes an empty result self-explanatory; it does not change how many findings the model produces.

738 tests · 15/15 eval scenarios · typecheck + lint clean.