feat(tests): archive round history on reopen, stop pausing from setting Jira On Hold

- Reopening a test for rework (red or blue) now archives the round that's
  ending into a new test_round_history table before resetting the live
  fields — procedure/results/detection data is preserved instead of
  overwritten, and Phase Timeline renders every past round alongside the
  current one, so Blue Team keeps visibility into earlier Red attempts.
- Each archived round also posts a permanent Jira comment (push_round_archived)
  since Jira's custom fields only ever show the latest value once the next
  round resubmits — the comment thread is what preserves full history there.
- push_pause_event no longer transitions the Jira issue to "On Hold" — a
  timer pause is not a real Hold, and flipping Jira status for it was
  misleading. Only the explicit Hold action (push_hold_event) does that now.

backend/app/models/__init__.py

@@ -43,6 +43,7 @@ from app.models.evidence import Evidence
 from app.models.intel import IntelItem
 from app.models.technique import Technique
 from app.models.test import Test
+from app.models.test_round_history import TestRoundHistory
 from app.models.test_template import TestTemplate
 from app.models.user import User
 
@@ -86,4 +87,5 @@ __all__ = [
     "SsoConfig",
     "AlertRule",
     "AlertInstance",
+    "TestRoundHistory",
 ]