feat(ui): add confirmation for long timed runs

- Add confirmation dialog for runs 30+ minutes
- Show duration in human-readable format (hours/minutes)
- Replace alert with toast for empty prompt warning

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/web/public/app.js

@@ -773,10 +773,20 @@ class ClaudemanApp {
     }
 
     if (!prompt) {
-      alert('Please enter a prompt');
+      this.showToast('Please enter a prompt', 'warning');
       return;
     }
 
+    // Confirm for long runs (over 30 minutes)
+    if (duration >= 30) {
+      const hours = Math.floor(duration / 60);
+      const mins = duration % 60;
+      const timeStr = hours > 0 ? `${hours}h ${mins}m` : `${mins} minutes`;
+      if (!confirm(`Start a ${timeStr} timed run? This will use API credits for the duration.`)) {
+        return;
+      }
+    }
+
     this.setRunning(true);
     this.terminal.writeln('');
     this.terminal.writeln(`\x1b[1;36m─── Starting: ${prompt.substring(0, 60)}${prompt.length > 60 ? '...' : ''} ───\x1b[0m`);