fix(next/font): case insensitivity in local font extension check

[jozsefsallai]

Validating local fonts fails with an "Unexpected file" error if the extension in the provided font file's path is not lowercase (e.g. "MYFONT.WOFF"). This PR converts the path into all lowercase before checking it with the regex. I decided not to use the case insensitive regex flag to avoid breaking later logic that uses the result of the check.

A new unit test was also included to test for case insensitivity.

---

Somewhat related suggestion: the error message is a bit vague at the moment and it's not clear that the error happens due to an unsupported extension. It took me quite a bit to debug the issue when I faced it and I would've never realized why it happens if I didn't take a look at the source code 😅 Would be neat if the error message specifically pointed this out (and maybe even displayed a list of supported extensions).

[ijjk]

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[graphite-app]

The optional chaining on fontFile.path?.toLowerCase() protects against null/undefined values, but would still throw a TypeError if path is a non-string value (like a number or object). Consider adding type checking to handle all cases:

const ext = /\.(woff|woff2|eot|ttf|otf)$/.exec(
  typeof fontFile.path === 'string' ? fontFile.path.toLowerCase() : String(fontFile.path || '')
)?.[1]

This ensures the regex always runs against a string value, preventing potential runtime errors.

Suggested change

	const ext = /\.(woff|woff2|eot|ttf|otf)$/.exec(
	fontFile.path?.toLowerCase()
	)?.[1]
	const ext = /\.(woff|woff2|eot|ttf|otf)$/.exec(
	typeof fontFile.path === 'string' ? fontFile.path.toLowerCase() : String(fontFile.path || '')
	)?.[1]

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