Add indexes to optimize slow queries (#1618)

* Add indexes to optimize slow queries

* Remove redundant index and run PRAGMA optimize

crates/db/migrations/20251219164205_add_missing_indexes_for_slow_queries.sql

@@ -0,0 +1,14 @@
+CREATE INDEX IF NOT EXISTS idx_sessions_workspace_id_created_at
+ON sessions (workspace_id, created_at DESC);
+
+CREATE INDEX IF NOT EXISTS idx_projects_created_at
+ON projects (created_at DESC);
+
+CREATE INDEX IF NOT EXISTS idx_workspaces_container_ref
+ON workspaces (container_ref)
+WHERE container_ref IS NOT NULL;
+
+CREATE INDEX IF NOT EXISTS idx_eprs_process_repo
+ON execution_process_repo_states (execution_process_id, repo_id);
+
+PRAGMA optimize;