refactor(search): address PR #750 round 8 review feedback

- Rename `verified_count` → `verified_chunk_count` to make the count
  granularity explicit at the field name (chunks vs unique docs).
- News verifier now fails open *per-item* on non-numeric stored doc_ids
  (matches notes/files/deck shape); a single bad id no longer rescues
  definitively-missing siblings from eviction.
- Update note-verifier integration test to use string doc_ids end-to-end
  to match production storage (scanner.py:241 stringifies note ids).
- Add regression test for the closed-task-group race guard in
  `verify_search_results` so the RuntimeError swallow is locked in.
- Convert remaining f-string logger calls in `server/semantic.py` to
  lazy %-style formatting (per repo convention).
- Document `evict_on_missing` as a developer/test flag (no env var) and
  flag the `get_file_info` 404→raise contract change in its docstring.
- Add a TODO(ADR-019) breadcrumb for the hardcoded 2× over-fetch so
  future tuning has a clear hook.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/configuration.md

@@ -513,9 +513,11 @@ aware of:
   (fail open) so a flaky link does not silently shrink result pages; only
   *definitive* 404 / 403 drops them.
 
-If verification ever needs to be disabled (debugging, benchmarking), the
-`evict_on_missing=False` flag on `verify_search_results()` skips eviction
-without changing what is returned to the caller.
+If eviction ever needs to be disabled (debugging, benchmarking), the
+`evict_on_missing=False` keyword argument on `verify_search_results()` skips
+the Qdrant deletes without changing what is returned to the caller. **This
+is a developer/test flag, not an operator knob — it has no env-var
+equivalent.** Operators who need a runtime toggle should open an issue.
 
 ### Environment Variables Reference