feat(runner): queue workflow runs with BullMQ (phase A)

Enqueue HTTP, cron, and manual runs via Redis/BullMQ; workers execute
asynchronously with configurable concurrency. Triggers return 202 and
clients poll GET /api/runs/:id for progress (queued → running → done).

Co-authored-by: Nasyarobby Putra <nasyarobby@gmail.com>

packages/server/migrations/20260819040000_workflow_run_queue.js

@@ -0,0 +1,24 @@
+/**
+ * @param {import("knex").Knex} knex
+ */
+export async function up(knex) {
+  await knex.schema.alterTable("workflow_runs", (t) => {
+    t.text("job_id");
+    t.text("queued_at");
+  });
+
+  await knex.schema.raw(
+    "CREATE INDEX workflow_runs_job_id_idx ON workflow_runs (job_id)",
+  );
+}
+
+/**
+ * @param {import("knex").Knex} knex
+ */
+export async function down(knex) {
+  await knex.schema.raw("DROP INDEX IF EXISTS workflow_runs_job_id_idx");
+  await knex.schema.alterTable("workflow_runs", (t) => {
+    t.dropColumn("job_id");
+    t.dropColumn("queued_at");
+  });
+}