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/models/semantic.py

@@ -10,7 +10,7 @@ from .base import BaseResponse
 class SemanticSearchResult(BaseModel):
     """Model for semantic search results with additional metadata."""
 
-    id: int = Field(description="Document ID")
+    id: int = Field(description="Document ID (int for all document types)")
     doc_type: str = Field(
         description="Document type (note, calendar_event, deck_card, etc.)"
     )