feat: refactor multi-code boxing UI with compact v2 layout

Merge box number and paichan info into a single header bar,
compress list rows to 40px with left color bars, fix bottom
operation area (scan/submit/finish) above status bar, and
shrink notification bars and status bar for more list space.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/widgets/status_bar.dart

@@ -33,23 +33,23 @@ class StatusBar extends StatelessWidget {
     final colorScheme = Theme.of(context).colorScheme;
     return Container(
       width: double.infinity,
-      padding: const EdgeInsets.symmetric(vertical: 12, horizontal: 16),
+      padding: const EdgeInsets.symmetric(vertical: 6, horizontal: 12),
       color: colorScheme.surfaceContainerHighest,
       child: Row(
         children: [
           Container(
-            width: 8,
-            height: 8,
+            width: 7,
+            height: 7,
             decoration: BoxDecoration(
               color: _resolveDotColor(context),
               shape: BoxShape.circle,
             ),
           ),
-          const SizedBox(width: 8),
+          const SizedBox(width: 7),
           Expanded(
             child: Text(
               text,
-              style: const TextStyle(fontSize: 14),
+              style: const TextStyle(fontSize: 12),
               overflow: TextOverflow.ellipsis,
             ),
           ),