feat: use checksummed filenames for recipe images and clean up old files

Updated recipe image handling to use checksummed filenames for proper
cache busting. When uploading a new image during recipe edit, old image
files (both hashed and unhashed versions) are now properly deleted from
all directories (full, thumb, placeholder).

Changes:
- CardAdd.svelte: Use checksummed filename from upload response
- Edit page server: Add deleteRecipeImage() helper to remove old images
- Edit page server: Delete old images when new image is uploaded

src/lib/components/CardAdd.svelte

@@ -113,7 +113,7 @@ export async function show_local_image(){
 		}
 
 		const result = await response.json();
-		uploaded_image_filename = result.unhashedFilename;
+		uploaded_image_filename = result.filename;
 		upload_error = "";
 
 	} catch (error: any) {