chore: remove Airflow completely from the stack

Drop all four Airflow containers (db, init, webserver, scheduler) from the
mlops compose profile, leaving MLflow as the sole mlops service. Remove
AIRFLOW_* env vars, config fields, health-check entries, DAG trigger code
in admin/bench routes, the airflow_dag_run_id schema column, Airflow nav
links and DAG-run links in the admin UI, the two Airflow DAG files
(bench_dag.py, sim_dag.py), and all related docs/ADR references.
Simulations now run exclusively via the subprocess path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/admin/src/lib/api.ts

@@ -278,7 +278,6 @@ export interface SimRun {
   summaryJson: string | null;
   winner: string | null;
   personaBreakdownJson: string | null;
-  airflowDagRunId: string | null;
   mlflowRunId: string | null;
   createdAt: string;
   finishedAt: string | null;
@@ -293,7 +292,7 @@ export interface SimStartRequest {
 }
 
 export function startSimulation(req: SimStartRequest) {
-  return apiFetch<{ id: string; status: string; airflow_dag_run_id?: string }>(
+  return apiFetch<{ id: string; status: string }>(
     '/admin/simulate/start',
     { method: 'POST', body: JSON.stringify(req) },
   );