feat: harmonize MCP tool + userinfo page to documents/chunks model

Extend the documents-vs-chunks split to the remaining status surfaces so all
three report consistently (Deck #195):

- nc_get_vector_sync_status MCP tool + VectorSyncStatusResponse: add
  indexed_documents (distinct) and indexed_chunks; keep indexed_count as a
  deprecated alias of indexed_chunks. Reuses count_indexed.
- userinfo HTML page (/app/vector-sync/status): show Indexed Documents AND
  Indexed Chunks rows; switch its count to count_indexed (which also excludes
  placeholder points — the old raw count included them).
- /api/v1/vector-sync/status: restore indexed_count as a deprecated alias of
  indexed_chunks so existing consumers (integration tests, pre-#115 UI) keep
  working; the change is now purely additive for indexed_count.

Tests: VectorSyncStatusResponse documents/chunks/alias + zeroed defaults.

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

nextcloud_mcp_server/models/semantic.py

@@ -153,14 +153,26 @@ class VectorSyncStatusResponse(BaseResponse):
     including how many documents are indexed and how many are pending.
 
     Attributes:
-        indexed_count: Number of documents in Qdrant vector database
+        indexed_documents: Distinct documents indexed in the vector database
+        indexed_chunks: Total indexed chunks (vector points); ~N per document
+        indexed_count: DEPRECATED alias of indexed_chunks
         pending_count: Number of documents in processing queue
         status: Current sync status ("idle" or "syncing")
         enabled: Whether vector sync is enabled
     """
 
+    indexed_documents: int = Field(
+        default=0, description="Distinct documents indexed in the vector database"
+    )
+    indexed_chunks: int = Field(
+        default=0, description="Total indexed chunks (vector points); ~N per document"
+    )
     indexed_count: int = Field(
-        default=0, description="Number of documents indexed in vector database"
+        default=0,
+        description=(
+            "DEPRECATED alias of indexed_chunks (the chunk/point count). Use "
+            "indexed_documents for the distinct-document count."
+        ),
     )
     pending_count: int = Field(
         default=0, description="Number of documents pending processing"