feat(accounting): invoices force-enable the Accounting master

Invoice VAT config (codes + label) and the hourly rate now live under
Settings → Accounting, so an install with Invoices must have Accounting
available.

- applyDependencyRules (backend adminFeatureFlags.js + frontend
  FeatureFlagsContext.tsx): bills on → accounting on, before the
  accounting→children rule so the sub-features keep their own state.
- Migration 133 corrects existing installs: set the STORED accounting=true
  where bills is on. requireFeatureFlag('accounting') reads the raw row, so
  without this an upgraded install (invoices on, accounting off) would show
  the tab but 403 its endpoints. Idempotent; only flips on; no down.
- Features tab: the Accounting card shows locked-on (disabled + hint) while
  Invoices is enabled.

Also includes the i18n keys (en/de) for the VAT/financial settings move.

frontend/src/contexts/FeatureFlagsContext.tsx

@@ -91,6 +91,10 @@ function applyDependencyRules(flags: FeatureFlags): FeatureFlags {
   out.galleries = true;                            // foundation — always on
   if (out.quotes === false) out.bills = false;     // bills depend on quotes
   if (out.calendar === false) out.calendarBooking = false;  // booking depends on calendar
+  // Invoices (Bills) force-enable the Accounting master — invoice VAT config +
+  // hourly rate live under Settings → Accounting. Before the accounting→children
+  // rule so sub-features keep their own state.
+  if (out.bills === true) out.accounting = true;
   // Accounting sub-features require the Accounting master. Tax export is
   // independent of Bills now — it relocated permanently into Accounting.
   if (out.accounting === false) {