feat(mileage): surface Körjournal in the nav behind a settings toggle (#1540)

* feat(mileage): surface Körjournal in the nav behind a settings toggle

The /mileage page shipped hidden: the route works but no nav row points at
it. Add company_settings.mileage_enabled (mirroring dimensions_enabled) with
a switch in Fönster -> Bokföring, and show the Arbeta nav row when the toggle
is on OR the company already has mileage_trips rows, the same hybrid gate as
webshop orders, so trips created via API/MCP can never become invisible
underlag. UI visibility only, never load-bearing for correctness.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(migrations): move mileage_enabled migration after already-applied 20260812153208

origin/main merged in 20260812153208 which prod has already applied; a new
file sorting before it risks an out-of-order db push abort.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

app/api/settings/__tests__/route.test.ts

@@ -97,6 +97,25 @@ describe('PUT /api/settings', () => {
     expect(deadlineMocks.regenerate).not.toHaveBeenCalled()
   })
 
+  it('accepts the mileage_enabled visibility toggle', async () => {
+    enqueueMany([
+      { data: { entity_type: 'enskild_firma', onboarding_complete: true } }, // fetch oldSettings
+      { data: { id: 's1', mileage_enabled: true } },                          // update ... returning
+      { data: null, count: 5 },                                               // deadlines count (has some -> no regen)
+    ])
+
+    const request = createMockRequest('/api/settings', {
+      method: 'PUT',
+      body: { mileage_enabled: true },
+    })
+    const response = await PUT(request, { params: Promise.resolve({}) })
+    const { status, body } = await parseJsonResponse<{ data: { mileage_enabled: boolean } }>(response)
+
+    expect(status).toBe(200)
+    expect(body.data.mileage_enabled).toBe(true)
+    expect(deadlineMocks.regenerate).not.toHaveBeenCalled()
+  })
+
   it('round-trips share capital fields and clears them with null', async () => {
     const updates = { aktiekapital: 25000, antal_aktier: 500 }
     enqueueMany([