feat(external-pr): surface in-flight reviews in the panel, not just completed

The PR-review queue only listed COMPLETED reviews and hid when empty, so while
a review was in_progress the panel showed nothing — no sign a review was
happening or where its findings go (the reviewer posts its change-request on
the PR itself). Add TaskService.list_external_pr_reviews (active reviews +
awaiting-decision, minus cancelled/decided/dismissed); the route uses it. The
panel card now shows active reviews with a 'Reviewing' badge and a link to the
PR where the change-request lands, and the Supersede/Dismiss actions only once
the review completes.

tests/unit/services/test_external_pr_ingest.py

@@ -76,6 +76,17 @@ async def test_list_awaiting_decision_excludes_dismissed() -> None:
     assert out == [pending]
 
 
+@pytest.mark.asyncio
+async def test_list_external_pr_reviews_excludes_dismissed() -> None:
+    # The panel queue surfaces in-flight reviews too (the status filter lives in
+    # SQL); here we pin the post-query behavior: dismissed reviews drop out.
+    reviewing = MagicMock(quick_context="external_pr_head=abc")
+    dismissed = MagicMock(quick_context="external_pr_head=def dismissed=1")
+    svc = _service([reviewing, dismissed])
+    out = await svc.list_external_pr_reviews()
+    assert out == [reviewing]
+
+
 @pytest.mark.asyncio
 async def test_dismiss_marks_and_is_idempotent() -> None:
     task = MagicMock(source="external_pr", quick_context="external_pr_head=abc")