feat: Album artwork generation via Gemini Image models

Backend:
- New image_gen.py module with Gemini image generation client
  - generate_artwork(): generates PNG from text prompt using Google GenAI
  - get_image_gen_config(): loads config from .env (model, API key, safety)
  - get_available_models(): returns list of Gemini image models
  - Safety settings: harassment, hate_speech, sexually_explicit, dangerous
    Configurable via IMAGE_GEN_SAFETY_* env vars (default: BLOCK_ONLY_HIGH)
- New endpoints:
  * POST /api/clips/{id}/generate-artwork — generates and saves artwork
  * GET /api/image-gen/models — lists available models
  * GET /api/image-gen/config — returns safe config (API key masked)
- Default model: gemini-3.1-flash-image-preview
- Fallback API key: LYRIA_API_KEY if IMAGE_GEN_API_KEY not set
- Added google-genai==1.0.0 to requirements.txt

Frontend:
- New ArtworkGenerationModal component for prompt input
  - Textarea with placeholder, loading spinner during generation
  - Styled consistent with SettingsModal (backdrop blur, rounded, dark)
- SettingsModal expanded with Image Generation section (collapsible)
  - Shows current model, API key status, safety filter levels
  - Read-only display — values configured via .env
- DetailPanel: 'Generate' button added next to Upload/Change
  - Passes onGenerateArtwork prop to App.tsx
- App.tsx: handles artwork generation flow, updates state on success

Architecture KB and Tasks KB updated.

backend/src/main.py

@@ -9,11 +9,14 @@ from dotenv import load_dotenv
 # Load environment variables BEFORE importing lyria_client (it reads env at module level)
 load_dotenv(Path(__file__).parent.parent / ".env")
 
-from models import GenerateRequest, GenerateResponse, ClipList, RenameRequest, LYRIA_MODELS, DEFAULT_MODEL
+from models import GenerateRequest, GenerateResponse, ClipList, RenameRequest, GenerateArtworkRequest, LYRIA_MODELS, DEFAULT_MODEL
 from database import init_db, create_clip, get_clips, get_clip, delete_clip, update_clip_status, rename_clip, set_artwork, remove_artwork, delete_all_clips, set_analysis
 from lyria_client import generate_clip, save_clip_file
 from waveform import generate_waveform_svg, get_waveform_path
 from analysis import analyze_clip
+from image_gen import generate_artwork, get_image_gen_config, get_available_models
+from analysis import analyze_clip
+from image_gen import generate_artwork, get_image_gen_config, get_available_models, SAFETY_LEVELS
 
 app = FastAPI(title="Lyria Studio", version="0.1.0")
 
@@ -243,6 +246,58 @@ async def remove_artwork_endpoint(clip_id: str):
     updated = await get_clip(clip_id)
     return updated
 
+@app.post("/api/clips/{clip_id}/generate-artwork")
+async def generate_clip_artwork(clip_id: str, request: GenerateArtworkRequest):
+    """Generate album artwork using Gemini Image model."""
+    clip = await get_clip(clip_id)
+    if not clip:
+        raise HTTPException(status_code=404, detail="Clip not found")
+
+    try:
+        # Generate image
+        config = get_image_gen_config()
+        image_bytes = await generate_artwork(request.prompt, config)
+
+        # Save to disk
+        import uuid
+        artwork_filename = f"{clip_id}_{uuid.uuid4().hex[:8]}.png"
+        artwork_path = ARTWORK_DIR / artwork_filename
+        with open(artwork_path, "wb") as f:
+            f.write(image_bytes)
+
+        # Remove old artwork if exists
+        if clip.get("artwork_filename"):
+            old_path = ARTWORK_DIR / clip["artwork_filename"]
+            if old_path.exists():
+                old_path.unlink()
+
+        # Update DB
+        await set_artwork(clip_id, artwork_filename)
+        updated = await get_clip(clip_id)
+        return updated
+
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=f"Image generation failed: {str(e)}")
+
+@app.get("/api/image-gen/models")
+async def list_image_gen_models():
+    """List available image generation models."""
+    return {"models": get_available_models()}
+
+@app.get("/api/image-gen/config")
+async def get_image_gen_configuration():
+    """Get current image generation configuration (safe values only)."""
+    config = get_image_gen_config()
+    return {
+        "model": config["model"],
+        "safety_harassment": config["safety_harassment"],
+        "safety_hate_speech": config["safety_hate_speech"],
+        "safety_sexually_explicit": config["safety_sexually_explicit"],
+        "safety_dangerous": config["safety_dangerous"],
+        # API key is masked
+        "has_api_key": bool(config.get("api_key")),
+    }
+
 @app.patch("/api/clips/{clip_id}")
 async def rename_clip_endpoint(clip_id: str, request: RenameRequest):
     clip = await get_clip(clip_id)