feat: sync execution with 3s progress polling (stage 2)

- pulp_client: get_repo / sync_repo / get_task (비동기 task href 반환)
- POST /repos/{uuid}/sync: remote 확인 후 동기화 시작, 진행률 조각 반환
- GET /repos/{uuid}/progress: progress_reports 합산 → 바/퍼센트,
  완료/실패 시 hx-trigger 제거로 폴링 중단
- task_store: uuid→task_href 메모리 추적 (단일 인스턴스), 대시보드 '동기화 중' 집계
- views.task_progress: state/done/total/percent + created_resources에서 새 vN
- 동기화는 안전 동작이라 확인 모달 없이 실행 (스펙 §5-1)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_pulp_client.py

@@ -37,3 +37,27 @@ def test_get_raises_on_http_error():
     )
     with PulpClient() as pulp, pytest.raises(httpx.HTTPStatusError):
         pulp.status()
+
+
+@respx.mock
+def test_sync_repo_posts_remote_and_returns_task():
+    import json
+
+    route = respx.post(
+        f"{PULP_TEST_URL}/pulp/api/v3/repositories/rpm/rpm/abc/sync/"
+    ).mock(return_value=httpx.Response(202, json={"task": "/pulp/api/v3/tasks/t1/"}))
+    with PulpClient() as pulp:
+        href = pulp.sync_repo("abc", "/pulp/api/v3/remotes/rpm/rpm/r1/")
+    assert href == "/pulp/api/v3/tasks/t1/"
+    body = json.loads(route.calls.last.request.content)
+    assert body == {"remote": "/pulp/api/v3/remotes/rpm/rpm/r1/"}
+
+
+@respx.mock
+def test_get_task_returns_state():
+    respx.get(f"{PULP_TEST_URL}/pulp/api/v3/tasks/t1/").mock(
+        return_value=httpx.Response(200, json={"state": "running"})
+    )
+    with PulpClient() as pulp:
+        task = pulp.get_task("/pulp/api/v3/tasks/t1/")
+    assert task["state"] == "running"