feat: admin survey responses page with expandable detail and CSV export

- Backend: GET /admin/survey-responses (list with stats, invite join)
- Backend: GET /admin/survey-responses/export (CSV download)
- Frontend: SurveyResponsesPage with expandable row detail
- Two-column Q&A grid with typed answer rendering (chips, ranked lists, quote blocks)
- Stats cards (total responses, this week)
- CSV export button with blob download
- Sidebar nav + route wiring
- Also: updated Q14 from product domain ranking to diagnostic prioritization

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

backend/tests/test_survey.py

@@ -113,3 +113,59 @@ async def test_create_and_list_invites(client, admin_auth_headers):
     assert list_res.status_code == 200
     invites = list_res.json()
     assert len(invites) >= 1
+
+
+@pytest.mark.asyncio
+async def test_list_survey_responses_admin(client, admin_auth_headers):
+    """Admin can list survey responses."""
+    await client.post(
+        "/api/v1/survey/submit",
+        json={"respondent_name": "Tester", "responses": {"q1": "answer"}},
+    )
+    res = await client.get("/api/v1/admin/survey-responses", headers=admin_auth_headers)
+    assert res.status_code == 200
+    data = res.json()
+    assert "responses" in data
+    assert "total" in data
+    assert "this_week" in data
+    assert data["total"] >= 1
+    assert data["responses"][0]["respondent_name"] == "Tester"
+    assert data["responses"][0]["source"] == "direct"
+
+
+@pytest.mark.asyncio
+async def test_list_survey_responses_requires_admin(client, auth_headers):
+    """Non-admin cannot list survey responses."""
+    res = await client.get("/api/v1/admin/survey-responses", headers=auth_headers)
+    assert res.status_code == 403
+
+
+@pytest.mark.asyncio
+async def test_export_survey_responses_csv(client, admin_auth_headers):
+    """Admin can export survey responses as CSV."""
+    await client.post(
+        "/api/v1/survey/submit",
+        json={
+            "respondent_name": "CSV Tester",
+            "responses": {
+                "prereqs": ["Who's affected", "What changed recently"],
+                "verify_fix": "Have the user confirm",
+                "steps_at_a_time": "5 steps",
+                "prioritization": ["Likelihood", "Speed", "Blast radius"],
+            },
+        },
+    )
+    res = await client.get("/api/v1/admin/survey-responses/export", headers=admin_auth_headers)
+    assert res.status_code == 200
+    assert "text/csv" in res.headers["content-type"]
+    assert "attachment" in res.headers.get("content-disposition", "")
+    body = res.text
+    assert "CSV Tester" in body
+    assert "Respondent" in body
+
+
+@pytest.mark.asyncio
+async def test_export_survey_responses_requires_admin(client, auth_headers):
+    """Non-admin cannot export survey responses."""
+    res = await client.get("/api/v1/admin/survey-responses/export", headers=auth_headers)
+    assert res.status_code == 403