fix(ui): WCAG light-theme accent, overflow-safe audit page, formal address

Accessibility/responsive audit pass with two new permanent test
gates (test/a11y_test.dart: WCAG text contrast + labeled tap
targets on every page in both themes; test/responsive_test.dart:
no layout overflow at 800/960/1280/1920 px). Findings fixed:

- Light theme primary/tertiary sky-500 → sky-700: white text on
  the lighter accent only reached 2.8:1 (welcome CTA, active
  sidebar label); sky-700 clears WCAG AA at ~5.9:1. Dark theme
  unchanged (already compliant). FABs now follow the same accent
  instead of Material 3's washed-out tonal default.
- Audit page: filter chips collapse into a checkmark popup menu
  below 900 px window width (app bar overflowed); the live-status
  bar's left text is now Expanded with ellipsis so the row can
  shrink, and the disconnected state's copyable error gets the
  full remaining width.
- German strings now use formal address consistently (~20 strings
  still used du-forms next to Sie-forms on welcome/setup), the
  audit event-type chip "Step" is "Schritt", and the doctor
  page's event count pluralises correctly in both languages.

flutter analyze clean, 64 tests green. Screenshot pass light+dark
via the guide-shots harness (verified parity, no overflows).

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_localizations.dart

@@ -2090,6 +2090,12 @@ abstract class AppLocalizations {
   /// **'module'**
   String get auditFilterModule;
 
+  /// No description provided for @auditFilterTooltip.
+  ///
+  /// In en, this message translates to:
+  /// **'Filter events'**
+  String get auditFilterTooltip;
+
   /// No description provided for @auditClearLogTooltip.
   ///
   /// In en, this message translates to:
@@ -3641,7 +3647,7 @@ abstract class AppLocalizations {
   /// No description provided for @doctorChainIntactDetail.
   ///
   /// In en, this message translates to:
-  /// **'{n} events · prev_event_sha256 verified end-to-end'**
+  /// **'{n} {n, plural, =1{event} other{events}} · prev_event_sha256 verified end-to-end'**
   String doctorChainIntactDetail(int n);
 
   /// No description provided for @doctorChainTampered.