fix(security): scope every HybridRAG leg and ingestion path to the caller's tenant

A live /query/hybrid probe as user=llm_tester returned jpmschweitzer
pages. Audit of all legs (vector, graph, web-persistence, volatile,
documents) plus enrichment/persistence found and fixed these unscoped
paths:

- vector_service.update_from_page and graph_service.update_from_page now
  refuse pages outside users/{user}/ - previously any tenant could
  ingest any wiki page (incl. another tenant's) into its own collection
  and graph labels, which is how foreign content entered the vector leg.
- ingestion_service.ingest_all_pages clamps path_prefix to the caller's
  namespace (segment-exact, sanitized comparison) and defaults to
  users/{user}; /ingest/all returns 400 on cross-tenant prefixes.
- hybrid_rag_service._persist_search_for_librarian linked SearchQuery
  nodes to unscoped (d:Document {page_id}); now matches only
  User_{Tenant}_Document nodes.
- graph_service: _get_entity_mention_count, entity-stub mention/related
  queries, generate_entity_stubs, find/purge_orphan_entities matched
  unscoped Document nodes; cleanup_broken_relationships matched all
  tenants' SearchQuery nodes; _entity_has_wiki_page listed all wiki
  pages. All are now tenant-label / namespace scoped.
- volatile_service collection names now use the sanitized user id.
- is_path_in_user_namespace enforces a path-segment boundary
  (users/llm_tester2 is not llm_tester's namespace) and treats
  hyphen/underscore tenant spellings as the same sanitized tenant.
- New offline unit tests per leg (mocked clients) assert the
  tenant-scoped collection/label/path is used and cross-tenant access
  is refused.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/services/vector_service.py

@@ -14,7 +14,7 @@ import logging
 from src.clients.qdrant_client import QdrantClientWrapper
 from src.clients.wikijs_client import WikiJSClient
 from src.clients.ollama_client import OllamaClient
-from src.core.multi_tenancy import get_qdrant_collection_name
+from src.core.multi_tenancy import get_qdrant_collection_name, is_path_in_user_namespace
 from src.models.vector import (
     SearchResult, SearchResponse, VectorUpdateSummary,
     DocumentChunk, CollectionInfo, CollectionListResponse
@@ -120,6 +120,16 @@ class VectorService:
             if not page:
                 raise ValueError(f"Page {page_id} not found")
 
+            # TENANT ISOLATION: only pages inside the user's own wiki
+            # namespace may be embedded into that user's collection.
+            # Without this check any tenant could ingest (and then read)
+            # another tenant's wiki content.
+            if not is_path_in_user_namespace(page.get("path", ""), user):
+                raise ValueError(
+                    f"Page {page_id} (path: {page.get('path')!r}) is outside "
+                    f"user '{user}' namespace - refusing cross-tenant ingestion"
+                )
+
             # Get collection name for user
             collection_name = get_qdrant_collection_name(user)