feat: enhance model caching and output modalities handling

- Updated `refresh_models_cache` to include output modalities in the models cache.
- Added `get_model_output_modalities` function to retrieve output modalities for a specific model.
- Modified tests to cover new functionality for output modalities.
- Updated OpenRouter video generation functions to support audio generation and improved error handling.
- Enhanced dashboard to display generated images and videos.
- Refactored frontend templates to accommodate new data structures for generated content.
- Adjusted tests to validate changes in model handling and dashboard rendering.

Co-authored-by: Copilot <copilot@github.com>

backend/tests/test_admin.py

@@ -53,7 +53,8 @@ async def test_stats_as_admin(client):
     resp = await client.get("/admin/stats", headers={"Authorization": f"Bearer {token}"})
     assert resp.status_code == 200
     data = resp.json()
-    assert data["users"]["total"] == 3  # 2 users + 1 admin
+    # 2 users + 1 admin + 1 seeded admin (ai@allucanget.biz)
+    assert data["users"]["total"] == 4
     assert "by_role" in data["users"]
     assert "refresh_tokens" in data