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>

nextcloud_mcp_server/models/semantic.py

@@ -80,16 +80,14 @@ class SemanticSearchResponse(BaseResponse):
     search_method: str = Field(
         default="semantic", description="Search method used (semantic or hybrid)"
     )
-    verified_count: int = Field(
+    verified_chunk_count: int = Field(
         default=0,
         description=(
             "Number of search result chunks that passed verify-on-read "
             "access checks (ADR-019). Equals len(verified_results) before "
-            "trimming to limit. Note: multiple chunks of the same document "
-            "are counted separately here, whereas dropped_count counts "
-            "unique (doc_id, doc_type) pairs — the asymmetry is intentional "
-            "(verified_count is sized in result rows, dropped_count is "
-            "sized in unique ghost documents)."
+            "trimming to limit. Sized in chunks (result rows), NOT in "
+            "unique documents — pair with dropped_count carefully: "
+            "dropped_count is sized in unique (doc_id, doc_type) pairs."
         ),
     )
     dropped_count: int = Field(