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>

lib/api/schemas.ts

@@ -1975,6 +1975,9 @@ export const UpdateSettingsSchema = z.object({
   // Dimensions (kostnadsställe/projekt): UI-visibility toggle only, never
   // load-bearing for correctness (dev_docs/dimensions_implementation_plan.md §2).
   dimensions_enabled: z.boolean().optional(),
+  // Körjournal (mileage log): UI-visibility toggle only, never load-bearing
+  // for correctness (trips created via API/MCP work regardless).
+  mileage_enabled: z.boolean().optional(),
   // Salary payment file
   preferred_payment_format: z.enum(['bg_lb', 'pain001']).optional(),
   // Salary settings (migration 20260703190000). Day of month salaries are