Completes the image-upload extraction (v0.4.12 did the immediate-save side).
components/_avatar_cropper is the deferred-form-field counterpart to
imageUploadHost: it stages a cropped PNG on a hidden file input + shows a round
preview, and the enclosing form (signup / profile edit) submits later.

Replace the old bespoke z-[110] crop overlay + direct cropper.js load +
avatarCropper() factory with avatarCropperHost(), which drives the crop through
the shared crop-photo modal + renders studio/cropper_assets. Parent gets the
cropped Blob via the crop-photo-confirmed window event. This is the version Turf
Monster had been running as a local override.

Bump 0.4.12 -> 0.4.13 + CHANGELOG + CLAUDE.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>