- Add /dashboard/profile/upload-pic/chunk endpoint: assembles chunks server-side,
  validates MIME type and 5 MB limit, base64-encodes and stores in DB + session
- Remove profile_pic from the form POST (was limited by proxy body size limits)
- Profile template: file input triggers JS chunked upload, shows progress bar and
  inline status; client-side pre-check for size/type before any network request
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>