refactor: Move background tasks to server lifespan and deprecate SSE transport

- Move scanner/processor tasks from FastMCP session lifespan to Starlette
  server lifespan (correct architecture: background tasks run once at
  server level, not per-session)
- Change default CLI transport from SSE to streamable-http
- Remove SSE transport option from CLI (SSE is deprecated)
- Remove SSE client session factory from test fixtures
- Add tracing instrumentation to BM25 hybrid search operations for
  better observability

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/conftest.py

@@ -9,7 +9,6 @@ import pytest
 from httpx import HTTPStatusError
 from mcp import ClientSession
 from mcp.client.session import RequestContext
-from mcp.client.sse import sse_client
 from mcp.client.streamable_http import streamablehttp_client
 from mcp.types import ElicitRequestParams, ElicitResult, ErrorData
 
@@ -172,51 +171,6 @@ async def create_mcp_client_session(
     logger.debug(f"{client_name} client session cleaned up successfully")
 
 
-async def create_mcp_client_session_sse(
-    url: str,
-    token: str | None = None,
-    client_name: str = "MCP",
-    elicitation_callback: Any = None,
-) -> AsyncGenerator[ClientSession, Any]:
-    """
-    Factory function to create an MCP client session using SSE transport.
-
-    Similar to create_mcp_client_session but uses SSE transport instead of streamable-http.
-    Uses native async context managers to ensure correct LIFO cleanup order.
-
-    Args:
-        url: MCP server URL (e.g., "http://localhost:8000/sse")
-        token: Optional OAuth access token for Bearer authentication
-        client_name: Client name for logging (e.g., "Basic MCP (SSE)")
-        elicitation_callback: Optional callback for handling elicitation requests
-
-    Yields:
-        Initialized MCP ClientSession
-
-    Note:
-        SSE transport is being deprecated in favor of streamable-http.
-        This function exists for compatibility testing only.
-    """
-    logger.info(f"Creating SSE client for {client_name}")
-
-    # Prepare headers with OAuth token if provided
-    headers = {"Authorization": f"Bearer {token}"} if token else None
-
-    # Use native async with - Python ensures LIFO cleanup
-    # Cleanup order will be: ClientSession.__aexit__ -> sse_client.__aexit__
-    # Note: sse_client yields only (read_stream, write_stream), not 3 values like streamablehttp_client
-    async with sse_client(url, headers=headers) as (read_stream, write_stream):
-        async with ClientSession(
-            read_stream, write_stream, elicitation_callback=elicitation_callback
-        ) as session:
-            await session.initialize()
-            logger.info(f"{client_name} client session initialized successfully")
-            yield session
-
-    # Cleanup happens automatically in LIFO order - no exception suppression needed
-    logger.debug(f"{client_name} client session cleaned up successfully")
-
-
 @pytest.fixture(scope="session")
 async def nc_client(anyio_backend) -> AsyncGenerator[NextcloudClient, Any]:
     """
@@ -255,18 +209,10 @@ async def nc_client(anyio_backend) -> AsyncGenerator[NextcloudClient, Any]:
 @pytest.fixture(scope="session")
 async def nc_mcp_client(anyio_backend) -> AsyncGenerator[ClientSession, Any]:
     """
-    Fixture to create an MCP client session for integration tests using SSE transport.
+    Fixture to create an MCP client session for integration tests using streamable-http.
 
     Uses anyio pytest plugin for proper async fixture handling.
-
-    Note: SSE transport is being deprecated. This fixture uses SSE for compatibility testing.
     """
-
-    # async for session in create_mcp_client_session_sse(
-    # url="http://localhost:8000/sse", client_name="Basic MCP (SSE)"
-    # ):
-    # yield session
-
     async for session in create_mcp_client_session(
         url="http://localhost:8000/mcp",
         client_name="Basic MCP (HTTP)",