fix: address PR #813 review (owner_id index, cache bound, explicit param)

- vector/qdrant_client.py: add owner_id to _PAYLOAD_INDEX_FIELDS (BLOCKING).
  Every search applies MatchAny(key="owner_id", ...); without a keyword index
  Qdrant full-scans the collection and may 400 on Qdrant Cloud strict mode.
  _ensure_payload_indexes is idempotent so existing collections migrate at
  startup.
- search/access_filter.py: bound the process-global _owners_cache with an LRU
  cap (was one unbounded entry per active user, never evicted); document the
  owner-level over-fetch limitation (a prolific sharer floods the recall
  buffer with ghost candidates that verify-on-read drops, with no second
  Qdrant pass) as a TODO toward per-file filtering.
- search/algorithms.py + semantic.py + bm25_hybrid.py: promote
  accessible_owners from **kwargs to an explicit keyword-only parameter on the
  SearchAlgorithm ABC and both implementations, so a misspelled keyword is a
  type error rather than a silent fall back to self-only scope.
- search/verification.py: document that _verify_files now verifies by global
  file id (WebDAV SEARCH), not by path.
- tests/unit/search/test_access_filter.py: add cache-hit, TTL-expiry,
  failure-not-cached, and LRU-bound tests.

Bumps the astrolabe submodule with the matching #89 review fixes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/search/algorithms.py

@@ -274,6 +274,8 @@ class SearchAlgorithm(ABC):
         user_id: str,
         limit: int = 10,
         doc_type: str | None = None,
+        *,
+        accessible_owners: list[str] | None = None,
         **kwargs: Any,
     ) -> list[SearchResult]:
         """Execute search with the given parameters.
@@ -283,6 +285,12 @@ class SearchAlgorithm(ABC):
             user_id: User ID for multi-tenant filtering
             limit: Maximum number of results to return
             doc_type: Optional document type filter (note, file, calendar, etc.)
+            accessible_owners: Owner UIDs the user is allowed to read (self plus
+                the owners of content shared with them), pre-computed from the
+                OCS Sharing API by the caller. Declared explicitly — rather than
+                buried in ``**kwargs`` — so a misspelled keyword is a type error
+                instead of a silent fall back to self-only scope. ``None`` means
+                self-only (``[user_id]``).
             **kwargs: Algorithm-specific parameters
 
         Returns: