Fixed Accept uppercase image extensions (.JPG/.JPEG) - #512

Description

Uploading a valid image whose filename has an UPPERCASE extension
(e.g. IMG_1234.JPG, PHOTO.JPEG — common for camera/iPhone exports)
was rejected with "The image field must have one of the following
extensions...", even though the file was a genuine image.

Root cause: IMAGE_ALLOWED_EXTENSIONS is lowercase and the extension
comparisons were case-sensitive, so "JPG" !== "jpg".

This affected two rules — the second is why a single-line fix would have
been incomplete (the error would have just moved from validation.extensions
to file-mime-extension-mismatch):

• packages/Webkul/Core/src/Rules/FileOrImageValidValue.php — lowercase
  the extension in the allowed-extensions in_array() check.
• packages/Webkul/Core/src/Rules/FileMimeExtensionMatch.php — lowercase
  the extension in the guessExtension() comparison.

Lowercasing is applied only inside the comparisons, so:

• already-lowercase uploads behave identically (zero behavior change),
• error messages and mime lookups are untouched,
• the mime-vs-extension security check still runs — a file whose real
  type doesn't match its extension is still rejected.

Impacted upload paths: product image/file attributes, category image
fields, attribute-option swatches, user profile image, and TinyMCE
rich-text uploads.

How To Test This?

1. Take any valid .jpg image and rename the extension to uppercase .JPG.
2. Upload it to a product Image attribute → it is now accepted.
3. Repeat with .JPEG and .PNG → accepted.
4. Confirm .jpg (lowercase) still uploads as before.
5. Negative check: rename a non-image file to .JPG (mismatched real
   type) → still rejected by the mime/extension check.

Checklist

• vendor/bin/pest passes locally
• vendor/bin/pint --test reports no style issues
• Tailwind classes are reordered
• New user-facing strings use translation keys (all 33 locales)
• Target branch is master