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>

backend/app/domain/test_entity.py

@@ -314,21 +314,21 @@ class TestEntity:
     def check_dual_validation(self) -> None:
         """Evaluate both leads' votes and advance state if appropriate.
 
-        - Both **approved** -> ``validated``
-        - Either **rejected** -> ``rejected``
-        - Otherwise no change (waiting for the other lead).
+        Rules (v2 — consensus required):
+        - Both **approved**  -> ``validated``
+        - Both **rejected**  -> ``rejected``
+        - One approved + one rejected -> ``disputed`` (conflict, needs discussion)
+        - Otherwise (one or both still pending) -> no change
 
         Called automatically by :meth:`validate_red` and :meth:`validate_blue`.
-        Also available as a standalone entry point for backward compatibility
-        when validation fields are set externally.
         """
         self._check_dual_validation()
 
     def _assert_in_review(self, side: str) -> None:
-        if self.state != TestState.in_review:
+        if self.state not in (TestState.in_review, TestState.disputed):
             raise InvalidOperationError(
                 f"Cannot validate {side} side while test is in "
-                f"'{self.state.value}' state (must be in_review)"
+                f"'{self.state.value}' state (must be in_review or disputed)"
             )
 
     @staticmethod
@@ -339,11 +339,19 @@ class TestEntity:
             )
 
     def _check_dual_validation(self) -> None:
-        """If both leads have voted, advance to validated or rejected."""
+        """Advance the test state once both leads have voted."""
         r, b = self.red_validation_status, self.blue_validation_status
-        if r == "rejected" or b == "rejected":
-            self.state = TestState.rejected
-            self._events.append(DomainEvent("dual_validation_rejected"))
-        elif r == "approved" and b == "approved":
+
+        if r == "approved" and b == "approved":
             self.state = TestState.validated
             self._events.append(DomainEvent("dual_validation_approved"))
+
+        elif r == "rejected" and b == "rejected":
+            # Full consensus to reject
+            self.state = TestState.rejected
+            self._events.append(DomainEvent("dual_validation_rejected"))
+
+        elif (r == "approved" and b == "rejected") or (r == "rejected" and b == "approved"):
+            # Conflict: one approves, one rejects → needs discussion
+            self.state = TestState.disputed
+            self._events.append(DomainEvent("dual_validation_disputed"))