perf(indexers): offload sync embed_text to thread across background workers

Connector kb_sync_services (gmail, onedrive, google_calendar, jira),
streaming indexers (discord, luma, teams) and the file-processor save
path all called embed_text inside async coroutines, blocking the
background worker's event loop for the duration of the embed. Wrap each
call site in asyncio.to_thread so concurrent indexing tasks stop
serialising on the embed.

surfsense_backend/app/tasks/connector_indexers/discord_indexer.py

@@ -670,7 +670,9 @@ async def index_discord_messages(
 
                 # Heavy processing (embeddings, chunks)
                 chunks = await create_document_chunks(item["combined_document_string"])
-                doc_embedding = embed_text(item["combined_document_string"])
+                doc_embedding = await asyncio.to_thread(
+                    embed_text, item["combined_document_string"]
+                )
 
                 # Update document to READY with actual content
                 document.title = f"{item['guild_name']}#{item['channel_name']}"

surfsense_backend/app/tasks/connector_indexers/luma_indexer.py

@@ -6,6 +6,7 @@ Implements 2-phase document status updates for real-time UI feedback:
 - Phase 2: Process each event: pending → processing → ready/failed
 """
 
+import asyncio
 import time
 from collections.abc import Awaitable, Callable
 from datetime import datetime, timedelta
@@ -465,7 +466,9 @@ async def index_luma_events(
                     summary_content = (
                         f"Luma Event: {item['event_name']}\n\n{item['event_markdown']}"
                     )
-                    summary_embedding = embed_text(summary_content)
+                    summary_embedding = await asyncio.to_thread(
+                        embed_text, summary_content
+                    )
 
                 chunks = await create_document_chunks(item["event_markdown"])
 

surfsense_backend/app/tasks/connector_indexers/teams_indexer.py

@@ -9,6 +9,7 @@ Uses 2-phase document status updates for real-time UI feedback:
 - Phase 2: Process each document: pending → processing → ready/failed
 """
 
+import asyncio
 import time
 from collections.abc import Awaitable, Callable
 from datetime import UTC, datetime
@@ -581,7 +582,9 @@ async def index_teams_messages(
 
                 # Heavy processing (embeddings, chunks)
                 chunks = await create_document_chunks(item["combined_document_string"])
-                doc_embedding = embed_text(item["combined_document_string"])
+                doc_embedding = await asyncio.to_thread(
+                    embed_text, item["combined_document_string"]
+                )
 
                 # Update document to READY with actual content
                 document.title = f"{item['team_name']} - {item['channel_name']}"