feat(tests): disputed state + fix timestamps on reopen

1. New 'disputed' state — one lead approved, the other rejected:
   - Both approved → validated (unchanged)
   - Both rejected → rejected (unchanged)
   - One approves + one rejects → disputed (new)
   - DB: ALTER TYPE teststate ADD VALUE 'disputed'
   - Notification sent to the approving lead explaining the conflict
     with the rejection notes

2. Disputed UI in TestDetailHeader:
   - Amber banner showing conflict + rejection reason from notes
   - 'Change Vote to Rejected' button for the lead who approved
   - Validation indicators shown for disputed state too

3. Fix timestamps on reopen (rejected → draft):
   - Keep red_started_at, blue_started_at etc. as historical record
   - Only clear paused_at defensively
   - Timestamps naturally update when test is re-executed

4. disputed badge (amber) added to all badge color maps

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

frontend/src/pages/CampaignDetailPage.tsx

@@ -55,6 +55,7 @@ const testStateColors: Record<string, string> = {
   in_review: "bg-blue-900/50 text-blue-400 border-blue-500/30",
   validated: "bg-green-900/50 text-green-400 border-green-500/30",
   rejected: "bg-red-900/50 text-red-400 border-red-500/30",
+  disputed: "bg-amber-900/50 text-amber-400 border-amber-500/30",
 };
 
 export default function CampaignDetailPage() {