refactor(search): address PR #750 round 4 review feedback

- Guard eviction_task_group.start_soon against shutdown race so a
  RuntimeError on a closed group never surfaces as a search error.
- Correct ADR-019 news_item row: there is no per-item REST endpoint;
  verification batches via get_items(batch_size=-1) and intersects.
- Modernize models/semantic.py typing to PEP 604 / lowercase generics
  per CLAUDE.md.

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

nextcloud_mcp_server/search/verification.py

@@ -462,7 +462,15 @@ async def verify_search_results(
 
         if eviction_task_group is not None:
             for doc_id, doc_type in inaccessible:
-                eviction_task_group.start_soon(evict, doc_id, doc_type)
+                # Guard against the lifespan task group having exited between
+                # the getattr() capture in server/semantic.py and this call —
+                # start_soon raises RuntimeError on a closed group, which
+                # would otherwise surface as a search error. Eviction is
+                # best-effort: the next query re-verifies and re-attempts.
+                try:
+                    eviction_task_group.start_soon(evict, doc_id, doc_type)
+                except Exception:
+                    logger.debug("Eviction task group closed; will retry on next query")
         else:
             async with anyio.create_task_group() as tg:
                 for doc_id, doc_type in inaccessible: