refactor(search): address PR #750 round 2 review feedback

Implements fire-and-forget eviction (ADR-019 §"Lazy eviction"): the
search response no longer waits on Qdrant deletes, instead spawning
evict() on a long-lived lifespan-owned task group. Falls back to inline
eviction in modes without vector sync and in unit tests.

Also: harden _verify_news_items against non-numeric ids (fail open
instead of crashing the verifier); document the get_file_info None-on-404
contract; add INDEXED_DOC_TYPES single source of truth in vector/scanner.py
referenced by the CI-guard test; write a Verify-on-Read Latency Budget
section in docs/configuration.md covering the unbounded news.get_items
fetch. Closes the two remaining ADR-019 implementation checklist items.

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

nextcloud_mcp_server/vector/scanner.py

@@ -29,6 +29,16 @@ from nextcloud_mcp_server.vector.qdrant_client import get_qdrant_client
 logger = logging.getLogger(__name__)
 
 
+# Single source of truth for which doc_types this scanner indexes. The verifier
+# registry in `search/verification.py` must cover every type listed here
+# (enforced by `tests/unit/search/test_verification.py`). Add a verifier in the
+# same PR that adds a new indexed doc_type, or accept ghost-record exposure for
+# that type (see ADR-019).
+INDEXED_DOC_TYPES: frozenset[str] = frozenset(
+    {"note", "file", "deck_card", "news_item"}
+)
+
+
 @dataclass
 class DocumentTask:
     """Document task for processing queue."""