Localize user-facing reason strings in setting resolution warnings

[Copilot]

The reason strings interpolated into notifyUserOfSettingErrors's l10n.t(...) warning templates were hard-coded English (for managerNotRegistered and pathCannotResolve), producing partially-localized notifications in non-English locales.

Changes

• getLocalizedReason(error) helper in src/features/interpreterSelection.ts — builds a fully localized reason from the structured kind (and configuredValue where needed). The English reason field is retained on SettingResolutionError for logs/diagnostics only.
• Warning messages — the three l10n.t(...) calls in notifyUserOfSettingErrors now interpolate getLocalizedReason(firstError) instead of firstError.reason.

function getLocalizedReason(error: SettingResolutionError): string {
    switch (error.kind) {
        case 'managerNotRegistered':
            return l10n.t("Environment manager '{0}' is not registered", error.configuredValue);
        case 'pathUnresolvedVariables':
            return l10n.t('Path contains unresolved variables');
        case 'pathCannotResolve':
            return l10n.t("Could not resolve interpreter path '{0}'", error.configuredValue);
        default:
            return error.reason;
    }
}