feat(frontend): show destination format badge, fix download size to reflect converted output

The download button was showing the input file's size (carried over
client-side from upload) instead of the actual converted file's size.
It now reads outputSizeBytes from the polled job status once done.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/pages/HomePage.jsx

@@ -80,7 +80,11 @@ export function HomePage() {
   async function handleConvert() {
     const validItems = pendingFiles.filter((item) => item.targetFormat);
     const jobs = await uploadFiles(validItems);
-    const jobsWithSize = jobs.map((job, i) => ({ ...job, size: validItems[i].file.size }));
+    const jobsWithSize = jobs.map((job, i) => ({
+      ...job,
+      size: validItems[i].file.size,
+      targetFormat: validItems[i].targetFormat,
+    }));
     setSubmittedJobs((current) => [...current, ...jobsWithSize]);
     setPendingFiles([]);
   }
@@ -117,9 +121,21 @@ export function HomePage() {
         <ul className="job-list">
           {submittedJobs.map((job, index) =>
             job.id ? (
-              <FileCard key={job.id} fileName={job.file} fileSize={job.size} jobId={job.id} />
+              <FileCard
+                key={job.id}
+                fileName={job.file}
+                fileSize={job.size}
+                targetFormat={job.targetFormat}
+                jobId={job.id}
+              />
             ) : (
-              <FileCard key={`${job.file}-${index}`} fileName={job.file} fileSize={job.size} initialError={job.error} />
+              <FileCard
+                key={`${job.file}-${index}`}
+                fileName={job.file}
+                fileSize={job.size}
+                targetFormat={job.targetFormat}
+                initialError={job.error}
+              />
             )
           )}
         </ul>