refactor(db): rename search_space_roles table to workspace_roles

Phase 1 (rename DB) commit 1h: rename the roles table and flip both
inbound FKs (memberships.role_id, invites.role_id), plus the matching
raw-SQL cleanup in the obsidian plugin test.

surfsense_backend/tests/integration/test_obsidian_plugin_routes.py

@@ -129,7 +129,7 @@ async def race_user_and_space(async_engine):
             {"id": space_id},
         )
         await cleanup.execute(
-            text("DELETE FROM search_space_roles WHERE workspace_id = :id"),
+            text("DELETE FROM workspace_roles WHERE workspace_id = :id"),
             {"id": space_id},
         )
         await cleanup.execute(