Fix template literal syntax in thumbnail cleanup

The processThumbnailDeletion function in src/cleanup/processors.ts
had template literals that were incorrectly using double quotes,
preventing interpolation.  It also used non-existent variable names
thumbnailUrl and storageUrlBase in error messages, which has been
fixed to use medium.thumbnailUrl and STORAGE_URL_BASE.

Assisted-by: Gemini CLI:gemini-2.0-pro-exp-02-05

Author: dahlia

src/cleanup/processors.ts

@@ -38,10 +38,10 @@ export async function processThumbnailDeletion(
   if (reconstructedUrl !== medium.thumbnailUrl) {
     if (!medium.thumbnailUrl.startsWith(STORAGE_URL_BASE)) {
       throw new Error(
-        "The thumbnail URL ${thumbnailUrl} does not match the storage URL pattern ${storageUrlBase}!",
+        `The thumbnail URL ${medium.thumbnailUrl} does not match the storage URL pattern ${STORAGE_URL_BASE}!`,
       );
     } else {
-      throw new Error("The thumbnail URL ${medium.thumbnailUrl} is malformed.");
+      throw new Error(`The thumbnail URL ${medium.thumbnailUrl} is malformed.`);
     }
   }