v7.6.6 — Phone uploads: the file is read and checked before it is sent

• Fix - Uploading a photo or screenshot from a phone could fail with "Upload does not match what was declared": the browser sometimes hands over an empty file when the upload is sent. Customer Chat and the Staff AI console now read the file into memory and check its size before uploading, so a file the phone can no longer read is reported clearly instead of failing after the upload.
• Tweak - Tested up to WordPress 7.1.