fix: Update models and viz to use int-only doc_id

- algorithms.py: Revert SearchResult.id to int (all docs use int IDs now)
- semantic.py: Revert SemanticSearchResult.id to int, remove Union import
- viz_routes.py: Remove str() conversion when querying doc_id from Qdrant
- viz_routes.py: Convert doc_id from query param to int in chunk context

Fixes vector visualization which was collapsing all chunks to a single
point because Qdrant queries were failing to match doc_id (string vs int).

nextcloud_mcp_server/search/algorithms.py

@@ -123,7 +123,7 @@ class SearchResult:
     """A single search result with metadata and score.
 
     Attributes:
-        id: Document ID
+        id: Document ID (int for all document types)
         doc_type: Document type (note, file, calendar, contact, etc.)
         title: Document title
         excerpt: Content excerpt showing match context