refactor: extract consistent AppBar builder, remove icon from EVENT LOG title

- Add buildTracPulseAppBar() helper in lib/app_bar.dart
  - Reads backgroundColor/elevation from ThemeData.appBarTheme
  - Consistent back button (#9e9e9e, size 20) via Navigator.pop
  - Monospace title style (14px, weight 700, letter-spacing 2)
  - Optional onTitleTap for tappable titles
- Update all screens to use the new helper, removing redundant overrides
- Remove terminal icon from status_screen title, use plain centered text
- Change appBarTheme centerTitle to false (left-aligned)
- Remove bottom dividers from all screens

lib/main.dart

@@ -38,7 +38,7 @@ class TracPulseApp extends StatelessWidget {
           secondary: Color(0xFF00e676),
         ),
         appBarTheme: const AppBarTheme(
-          centerTitle: true,
+          centerTitle: false,
           backgroundColor: Color(0xFF161616),
           foregroundColor: Color(0xFFe0e0e0),
           elevation: 0,