[Designer] #215 Polish AI settings + frame suggestion surfaces

- frame_suggestion_dialog: hide exception detail in error path, redesign
  candidate card as Card+InkWell with L2/L3 colored level badge (secondary
  vs primary), remove confidence % surface.
- settings_screen: download tile gains state label + colored progress text,
  rounded LinearProgressIndicator, FilledButton.tonalIcon for resume/retry.
  _friendlyError() maps internal codes (network:/http /stream:/sha mismatch)
  to user-readable Korean. Opt-in/out dialogs reorganized with _Bullet rows;
  beta disclaimer reworded; _describe() friendlier copy.

Polish only — no behavior change. analyze 0, 71 tests pass, APK 10.3s.

Refs #215

app/lib/ui/widgets/frame_suggestion_dialog.dart

@@ -33,9 +33,11 @@ class FrameSuggestionDialog extends ConsumerWidget {
             height: 120,
             child: Center(child: CircularProgressIndicator()),
           ),
-          error: (e, _) => Padding(
-            padding: const EdgeInsets.all(8),
-            child: Text('AI 제안을 받지 못했습니다. 직접 입력해주세요.\n($e)'),
+          error: (e, _) => const Padding(
+            padding: EdgeInsets.all(8),
+            child: Text(
+              'AI 제안을 받지 못했어요.\n직접 입력하셔도 괜찮습니다.',
+            ),
           ),
           data: (candidates) {
             if (candidates.isEmpty) {
@@ -88,14 +90,49 @@ class _CandidateCard extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final scheme = Theme.of(context).colorScheme;
+    final isL3 = candidate.level == FrameLevel.l3;
+    final levelLabel = isL3 ? '정체성' : '조건부 긍정';
+    final levelCode = isL3 ? 'L3' : 'L2';
+    final levelColor = isL3 ? scheme.primary : scheme.secondary;
     return Card(
-      child: ListTile(
-        title: Text(candidate.framedText),
-        subtitle: Text(
-          '${candidate.level == FrameLevel.l3 ? "L3 · 정체성" : "L2 · 조건부 긍정"} '
-          '· 신뢰도 ${(candidate.confidence * 100).toInt()}%',
-        ),
+      margin: const EdgeInsets.symmetric(vertical: 4),
+      child: InkWell(
         onTap: onTap,
+        borderRadius: BorderRadius.circular(8),
+        child: Padding(
+          padding: const EdgeInsets.fromLTRB(12, 10, 12, 12),
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              Row(
+                children: [
+                  Container(
+                    padding:
+                        const EdgeInsets.symmetric(horizontal: 6, vertical: 2),
+                    decoration: BoxDecoration(
+                      color: levelColor.withValues(alpha: 0.12),
+                      borderRadius: BorderRadius.circular(4),
+                    ),
+                    child: Text(
+                      '$levelCode · $levelLabel',
+                      style: TextStyle(
+                        fontSize: 11,
+                        color: levelColor,
+                        fontWeight: FontWeight.w600,
+                      ),
+                    ),
+                  ),
+                ],
+              ),
+              const SizedBox(height: 6),
+              Text(
+                candidate.framedText,
+                style: Theme.of(context).textTheme.bodyLarge,
+              ),
+            ],
+          ),
+        ),
       ),
     );
   }