fix: restore post-v1.1.14 features while preserving asset updates

Undo the full-tree rollback in 6ea1b3d and restore the pre-rollback v1.2.0 code. Preserve the new asset flow rules, abnormal inventory separation, range drilldowns and date picker; adapt the regression test to the restored routes layout.

src/server/routes/vehicles/flow.test.ts

@@ -1,6 +1,6 @@
 import assert from 'node:assert/strict';
 import test from 'node:test';
-import router from '../vehicles.js';
+import router from './routes.js';
 import { vehicleRepository, type FlowDetailRow } from './repository.js';
 import type { Vehicle } from '../../types.js';