On Windows, mimetypes.guess_type() reads the Content Type value from
HKEY_CLASSES_ROOT\.js (and other extensions) in the registry, which is
commonly set to text/plain because .js is associated with Windows Script
Host rather than web JavaScript. The registry value overrides Python's
built-in mapping and causes browsers to reject ES module scripts.
Fix by explicitly registering correct MIME types via mimetypes.add_type()
at module import time for common web static extensions (.js, .mjs, .css,
.html, .json, .svg, .wasm). Using strict=True ensures the values replace
the registry-backed standard mappings used by mimetypes.guess_type(). This
benefits all callers of mimetypes.guess_type() in the gateway process, not
just _serve_static.
Closes#5190
Co-authored-by: amkile <44280409+amkile@users.noreply.github.com>
