fix: encode unicode filenames in Content-Disposition headers

Filenames with Romanian characters (Ș, Ț, etc.) caused ByteString errors.
Also pass original filename through to extreme mode response.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/api/compress-pdf/cloud/route.ts

@@ -195,7 +195,7 @@ export async function POST(req: NextRequest) {
       status: 200,
       headers: {
         "Content-Type": "application/pdf",
-        "Content-Disposition": `attachment; filename="${upload.filename.replace(/\.pdf$/i, "-comprimat.pdf")}"`,
+        "Content-Disposition": `attachment; filename="${encodeURIComponent(upload.filename.replace(/\.pdf$/i, "-comprimat.pdf"))}"`,
         "X-Original-Size": String(originalSize),
         "X-Compressed-Size": String(compressedSize),
       },

src/app/api/compress-pdf/extreme/route.ts

@@ -42,6 +42,7 @@ function streamFileResponse(
   filePath: string,
   originalSize: number,
   compressedSize: number,
+  filename: string,
 ): NextResponse {
   const nodeStream = createReadStream(filePath);
   const webStream = Readable.toWeb(nodeStream) as ReadableStream;
@@ -51,7 +52,7 @@ function streamFileResponse(
     headers: {
       "Content-Type": "application/pdf",
       "Content-Length": String(compressedSize),
-      "Content-Disposition": 'attachment; filename="optimized.pdf"',
+      "Content-Disposition": `attachment; filename="${encodeURIComponent(filename)}"`,
       "X-Original-Size": String(originalSize),
       "X-Compressed-Size": String(compressedSize),
     },
@@ -128,13 +129,13 @@ export async function POST(req: NextRequest) {
 
     // Stream result from disk — if bigger, stream original
     if (compressedSize >= originalSize) {
-      return streamFileResponse(inputPath, originalSize, originalSize);
+      return streamFileResponse(inputPath, originalSize, originalSize, upload.filename);
     }
 
     // NOTE: cleanup is deferred — we can't delete files while streaming.
     // The files will be cleaned up by the OS temp cleaner or on next request.
     // For immediate cleanup, we'd need to buffer, but that defeats the purpose.
-    return streamFileResponse(outputPath, originalSize, compressedSize);
+    return streamFileResponse(outputPath, originalSize, compressedSize, upload.filename);
   } catch (err) {
     const message = err instanceof Error ? err.message : "Unknown error";
     console.error(`[compress-pdf] Error:`, message);