feat: engineer SBAS timeseries production workflow

backend/migrations/007_timeseries_stack_plan_trace.sql

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+-- Additive indexes for the phase-2 timeseries stack plan trace chain.
+-- Tables/columns are created by SQLAlchemy metadata and db_maintenance missing-column repair.
+
+CREATE INDEX IF NOT EXISTS idx_ps_task_batches_plan_id
+    ON ps_task_batches (plan_id);
+
+CREATE INDEX IF NOT EXISTS idx_ps_task_items_plan_item_ref_id
+    ON ps_task_items (plan_item_ref_id);
+
+CREATE INDEX IF NOT EXISTS idx_ps_timeseries_runs_plan_id
+    ON ps_timeseries_runs (plan_id);
+
+CREATE INDEX IF NOT EXISTS idx_timeseries_stack_plans_request_hash
+    ON timeseries_stack_plans (request_hash);
+
+CREATE INDEX IF NOT EXISTS idx_timeseries_stack_plan_items_radar_ref
+    ON timeseries_stack_plan_items (radar_data_ref_id);