✨ Profile photo crop and preview before upload

[fusion94]

Summary

Profile.jsx currently uploads any chosen image at its original aspect ratio, which produces lopsided avatars. Add an in-browser crop step so members commit to a square JPEG before the upload happens.

Proposed Approach

1. Add react-easy-crop (or equivalent — small dep, ~30KB).
2. When the user picks a file, open a modal showing the image with a square crop overlay.
3. On confirm, render the cropped region to a canvas, convert to a JPEG Blob, and POST that instead of the original file.
4. Show the result in the Profile preview before the user clicks Save.

Acceptance Criteria

• Picking a file opens a crop modal, not an immediate upload.
• User can drag and zoom inside the crop window.
• Confirming uploads a square JPEG <= the existing 5MB limit.
• Cancel returns to the profile without uploading.
• Existing avatars continue to work (no migration needed).