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>

frontend/app/main.py

@@ -178,7 +178,13 @@ def dashboard():
     user = resp.json() if resp.status_code == 200 else {}
     img_resp = _api("GET", "/images/", token=token)
     images = img_resp.json() if img_resp.status_code == 200 else []
-    return render_template("dashboard.html", user=user, images=images)
+    gen_resp = _api("GET", "/generate/images", token=token)
+    generated_images = gen_resp.json() if gen_resp.status_code == 200 else []
+    vid_resp = _api("GET", "/generate/videos", token=token)
+    generated_videos = vid_resp.json() if vid_resp.status_code == 200 else []
+    return render_template("dashboard.html", user=user, images=images,
+                           generated_images=generated_images,
+                           generated_videos=generated_videos)
 
 
 # ── Generate ──────────────────────────────────────────────────────────────