feat: add error recovery with retry functionality

Error recovery features:
- **Retry button**: Appears on failed conversions
- **Smart retry logic**: Re-attempts conversion with same settings
- **State management**: Properly resets job state before retry
- **Progress tracking**: Shows progress during retry attempt
- **Toast notifications**: Informs user of retry success/failure
- **History updates**: Successful retries added to history
- **Visual feedback**: RefreshCw icon with clear button label

Implementation:
- Added onRetry prop to ConversionPreview component
- Implemented handleRetry function in FileConverter
- Reuses existing conversion logic for consistency
- Maintains all conversion options during retry
- Updates job status through proper state flow:
  error → loading → processing → completed/error

User experience:
- One-click retry for failed conversions
- No need to re-upload file or reconfigure settings
- Clear visual indication when retry is in progress
- Helpful error messages if retry also fails

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

components/converter/FileConverter.tsx

@@ -244,6 +244,109 @@ export function FileConverter() {
     addToast(`Downloaded ${files.length} files as ZIP`, 'success');
   };
 
+  const handleRetry = async (jobId: string) => {
+    const jobIndex = conversionJobs.findIndex(j => j.id === jobId);
+    if (jobIndex === -1 || !outputFormat) return;
+
+    const job = conversionJobs[jobIndex];
+
+    try {
+      // Reset job to loading
+      setConversionJobs((prev) =>
+        prev.map((j, idx) => idx === jobIndex ? {
+          ...j,
+          status: 'loading' as const,
+          progress: 0,
+          error: undefined,
+          startTime: Date.now(),
+        } : j)
+      );
+
+      // Update to processing
+      setConversionJobs((prev) =>
+        prev.map((j, idx) => idx === jobIndex ? { ...j, status: 'processing' as const, progress: 10 } : j)
+      );
+
+      // Call appropriate converter
+      let result;
+
+      switch (outputFormat.converter) {
+        case 'ffmpeg':
+          result = await convertWithFFmpeg(job.inputFile, outputFormat.extension, conversionOptions, (progress) => {
+            setConversionJobs((prev) =>
+              prev.map((j, idx) => idx === jobIndex ? { ...j, progress } : j)
+            );
+          });
+          break;
+
+        case 'imagemagick':
+          result = await convertWithImageMagick(
+            job.inputFile,
+            outputFormat.extension,
+            conversionOptions,
+            (progress) => {
+              setConversionJobs((prev) =>
+                prev.map((j, idx) => idx === jobIndex ? { ...j, progress } : j)
+              );
+            }
+          );
+          break;
+
+        default:
+          throw new Error(`Unknown converter: ${outputFormat.converter}`);
+      }
+
+      // Update job with result
+      if (result.success && result.blob) {
+        setConversionJobs((prev) =>
+          prev.map((j, idx) => idx === jobIndex ? {
+            ...j,
+            status: 'completed' as const,
+            progress: 100,
+            result: result.blob,
+            endTime: Date.now(),
+          } : j)
+        );
+
+        addToast('Conversion completed successfully!', 'success');
+
+        // Add to history
+        addToHistory({
+          inputFileName: job.inputFile.name,
+          inputFormat: job.inputFormat.name,
+          outputFormat: outputFormat.name,
+          outputFileName: `output.${outputFormat.extension}`,
+          fileSize: result.blob.size,
+          result: result.blob,
+        });
+      } else {
+        setConversionJobs((prev) =>
+          prev.map((j, idx) => idx === jobIndex ? {
+            ...j,
+            status: 'error' as const,
+            error: result.error || 'Unknown error',
+            endTime: Date.now(),
+          } : j)
+        );
+
+        addToast(result.error || 'Retry failed', 'error');
+      }
+    } catch (error) {
+      const errorMessage = error instanceof Error ? error.message : 'Unknown error';
+
+      setConversionJobs((prev) =>
+        prev.map((j, idx) => idx === jobIndex ? {
+          ...j,
+          status: 'error' as const,
+          error: errorMessage,
+          endTime: Date.now(),
+        } : j)
+      );
+
+      addToast(`Retry failed: ${errorMessage}`, 'error');
+    }
+  };
+
   const isConverting = conversionJobs.some(job => job.status === 'loading' || job.status === 'processing');
   const isConvertDisabled = selectedFiles.length === 0 || !outputFormat || isConverting;
   const completedCount = conversionJobs.filter(job => job.status === 'completed').length;
@@ -356,7 +459,11 @@ export function FileConverter() {
       {conversionJobs.length > 0 && (
         <div className="space-y-4">
           {conversionJobs.map((job) => (
-            <ConversionPreview key={job.id} job={job} />
+            <ConversionPreview
+              key={job.id}
+              job={job}
+              onRetry={() => handleRetry(job.id)}
+            />
           ))}
         </div>
       )}