fix: ignore path casing differences in Vite config override warning

[Nic-Polumeyv]

Fixes #16317, follow-up to #16037 which normalized separators for this warning but left the comparison case-sensitive. #16239 addressed the same casing issue with a per-key whitelist before it was closed alongside #16293.

During svelte-check, @sveltejs/load-config resolves the Vite config with an explicit root derived from directory traversal (loadSvelteConfigFromVite passes { root, configFile } and chdirs first), so the config SvelteKit's plugin receives always contains root, and it gets compared against SvelteKit's posixify(process.cwd()). The two strings match exactly on Linux, which is why the warning only ever shows on Windows, where the two routes can disagree on casing (typically the drive letter) and #16037's slash normalization doesn't help. That matches #16317 still reproducing on 2.69.2 after #16293 was closed as unreproducible on non-Windows. Windows paths are case-insensitive, so the comparison now folds case on win32.

Traced by instrumenting find_overridden_config, Vite's resolveConfig and runConfigHook in a fresh kit 2.69.2 + svelte-check 4.7.3 app. Validated by injecting a case-only difference into that flow, where the current comparison prints the reported warning, the fixed one stays silent, and a genuine appType override still warns. The reporter has since confirmed the case-only difference on real Windows in #16317 (comment). Like #16037 there is no test, the function is internal and the behaviour platform-specific.

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[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from d05ce41:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/d05ce4115b6005a5123d372277caa9a4cbfd7d4d

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16405

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Latest commit: d05ce41

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[Nic-Polumeyv]

Replaced by #16545 against version-3, since main is winding down.