feat: Editable safety settings in SettingsModal

Backend:
- New POST /api/image-gen/config endpoint to update image generation config
  in-memory (applies immediately, resets on server restart)
- Accepts: model, safety_harassment, safety_hate_speech,
  safety_sexually_explicit, safety_dangerous

Frontend:
- SettingsModal safety filters are now editable dropdowns (no longer disabled)
- Model selection is also editable
- Added 'Save Changes' button with visual feedback:
  * Green 'Settings saved!' on success
  * Red 'Failed to save' on error
  * Disabled when no changes made
- Tracks edited state vs. saved state
- Note: changes apply immediately but reset on server restart
  (set .env for persistence)

Fixed TypeScript issues:
- getConfigValue() properly typed to return string only
- Proper union type for config keys excluding has_api_key

backend/src/main.py

@@ -298,6 +298,23 @@ async def get_image_gen_configuration():
         "has_api_key": bool(config.get("api_key")),
     }
 
+@app.post("/api/image-gen/config")
+async def update_image_gen_configuration(request: dict):
+    """Update image generation configuration (in-memory only, not persisted to .env)."""
+    # Update environment variables in-memory for this process
+    if "model" in request:
+        os.environ["IMAGE_GEN_MODEL"] = request["model"]
+    if "safety_harassment" in request:
+        os.environ["IMAGE_GEN_SAFETY_HARASSMENT"] = request["safety_harassment"]
+    if "safety_hate_speech" in request:
+        os.environ["IMAGE_GEN_SAFETY_HATE_SPEECH"] = request["safety_hate_speech"]
+    if "safety_sexually_explicit" in request:
+        os.environ["IMAGE_GEN_SAFETY_SEXUALLY_EXPLICIT"] = request["safety_sexually_explicit"]
+    if "safety_dangerous" in request:
+        os.environ["IMAGE_GEN_SAFETY_DANGEROUS"] = request["safety_dangerous"]
+    
+    return {"status": "updated"}
+
 @app.patch("/api/clips/{clip_id}")
 async def rename_clip_endpoint(clip_id: str, request: RenameRequest):
     clip = await get_clip(clip_id)