refactor(search): address PR #750 review feedback

- Cap all_results to limit*2 after sort in the per-doc_types branch of
  nc_semantic_search to bound over-verification (was unbounded N-types).
- Switch BatchVerifier from (client, doc_ids, user_id) to (client, results,
  semaphore). Verifiers now read file paths and deck board/stack ids from
  SearchResult.metadata instead of doing fresh Qdrant scrolls — eliminates
  one duplicate round-trip per file/deck-card verification.
- Bound per-id verification concurrency with a shared anyio.Semaphore
  (default 20, matching server/semantic.py context-expansion convention).
  Prevents httpx pool exhaustion / rate limiting on large search pages.
- Propagate stack_id from Qdrant payload to SearchResult.metadata in both
  bm25_hybrid.py and semantic.py (board_id was already propagated).
- Drop now-unused _resolve_file_path / _resolve_deck_metadata helpers.
- Drop redundant int(d) in requested predicate from _verify_news_items.
- Rewrite eviction comment to be honest about inline (not background)
  execution and the resulting latency coupling.
- ADR-019 status: Proposed -> Accepted.
- Add news property to NextcloudClientProtocol.
- Widen SearchResult.id and SemanticSearchResult.id to int | str to match
  BatchVerifier signature and document support for future string-id types.
- Flip openWorldHint to True on nc_semantic_search_answer (it calls into
  Nextcloud via nc_semantic_search).

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

nextcloud_mcp_server/search/semantic.py

@@ -164,9 +164,14 @@ class SemanticSearchAlgorithm(SearchAlgorithm):
                 metadata["path"] = path
 
             # Add deck_card-specific metadata for frontend URL construction
+            # and verify-on-read (ADR-019) — both board_id and stack_id are
+            # required to call deck.get_card without an O(boards × stacks)
+            # iteration fallback.
             if doc_type == "deck_card":
                 if board_id := result.payload.get("board_id"):
                     metadata["board_id"] = board_id
+                if stack_id := result.payload.get("stack_id"):
+                    metadata["stack_id"] = stack_id
 
             # Return unverified results (verification happens at output stage)
             results.append(