refactor(search): address PR #750 round 3 review feedback

- _verify_deck_cards: hoist int(board_id|stack_id|doc_id) out of the generic
  except Exception into an explicit try/except (TypeError, ValueError) before
  the network call, mirroring _verify_news_items. Malformed payloads now log
  a specific warning instead of "unexpected error".
- _verify_news_items: add TODO(perf) above the get_items(batch_size=-1) call
  to mark the known fetch-all cost as a future profiling target.
- SemanticSearchResult.id: revert from int|str back to int. The internal
  SearchResult.id stays int|str for forward-compat; the MCP response model
  narrows at the boundary. server/semantic.py casts r.id to int when
  constructing the response so future string-id types fail loudly here
  instead of silently widening the public API.
- nc_semantic_search: replace the terse "extra for access filtering" comment
  with an ADR-019 NOTE block explaining the 2x over-fetch trade-off and the
  ghost-density under-delivery case (self-heals via lazy eviction).
- tests/integration/test_verify_on_read.py: extend the module docstring to
  call out that only the note verifier is exercised against real Nextcloud,
  while file/deck_card/news_item are unit-only — documenting the suite split
  for future contributors.
- ADR-019: rewrite "Module shape", "Verifier registry", example verifier,
  and "Deduplication" sections to match the shipped BatchVerifier interface
  (was per-id Verifier in the original draft). Add a "Why batch?" paragraph
  explaining the design choice. Update implementation checklist — every
  item is now [x] with corrected verifier names (plural) and the eviction
  module path (vector/eviction.py).

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

nextcloud_mcp_server/models/semantic.py

@@ -10,11 +10,13 @@ from .base import BaseResponse
 class SemanticSearchResult(BaseModel):
     """Model for semantic search results with additional metadata."""
 
-    id: int | str = Field(
+    id: int = Field(
         description=(
             "Document ID. Numeric for all currently indexed types (notes, files, "
-            "deck cards, news items); typed as int|str to allow future doc types "
-            "that use string identifiers."
+            "deck cards, news items). The internal SearchResult.id is typed as "
+            "int|str to leave room for future doc types with string identifiers; "
+            "the MCP response narrows to int and a future widening here would be "
+            "a deliberate, breaking-by-design API change."
         )
     )
     doc_type: str = Field(