Fix Unicode encoding in export headers for Chinese filenames

- Properly encode filenames with Chinese characters using RFC 6266
- Use filename*=UTF-8'' encoding in Content-Disposition headers
- Prevent latin-1 encoding errors when exporting files with Unicode titles

src/server/routers/api.py

@@ -96,18 +96,26 @@ def fetch_youtube_audio(payload: dict):
 @router.post("/export/transcript")
 def export_transcript(payload: TranscriptExportRequest):
     content, filename, mime_type = export_service.generate_transcript_export(payload)
+    # Properly encode filename for Content-Disposition header (RFC 6266)
+    import urllib.parse
+    encoded_filename = urllib.parse.quote(filename)
+    content_disposition = f"attachment; filename*=UTF-8''{encoded_filename}"
     return StreamingResponse(
         iter([content.encode("utf-8")]),
         media_type=mime_type,
-        headers={"Content-Disposition": f"attachment; filename={filename}"},
+        headers={"Content-Disposition": content_disposition},
     )
 
 
 @router.post("/export/summary")
 def export_summary(payload: SummaryExportRequest):
     content, filename, mime_type = export_service.generate_summary_export(payload)
+    # Properly encode filename for Content-Disposition header (RFC 6266)
+    import urllib.parse
+    encoded_filename = urllib.parse.quote(filename)
+    content_disposition = f"attachment; filename*=UTF-8''{encoded_filename}"
     return StreamingResponse(
         iter([content.encode("utf-8")]),
         media_type=mime_type,
-        headers={"Content-Disposition": f"attachment; filename={filename}"},
+        headers={"Content-Disposition": content_disposition},
     )