fix(ui): resolve light-theme low-contrast semantic text app-wide (#1909)

The app was built dark-first, so hundreds of hardcoded Tailwind semantic
text/icon utilities at light shades (text-amber-400, text-blue-300, ...) had
no dark: variant. With darkMode:'class' they applied in light theme too,
producing washed-out text on pale tints and white cards — including the three
reported spots (AMS Drying banner, Archives no-3MF warning, debug-logging
banner). Give each a theme-aware pair: a darker readable shade in light theme
with the original pinned to dark:, so dark theme is unchanged. ~100 files.

The bambu-* CSS-variable palette (self-correcting) and the dark-only SpoolBuddy
kiosk are left untouched. Plain text-white is already theme-aware via the
existing index.css .text-white override, so it needed no changes.

frontend/src/components/AddNotificationModal.tsx

@@ -284,7 +284,7 @@ export function AddNotificationModal({ provider, onClose }: AddNotificationModal
         {/* Form */}
         <form onSubmit={handleSubmit} className="p-6 space-y-4">
           {error && (
-            <div className="p-3 bg-red-500/20 border border-red-500/50 rounded-lg text-sm text-red-400">
+            <div className="p-3 bg-red-100 dark:bg-red-500/20 border border-red-300 dark:border-red-500/50 rounded-lg text-sm text-red-700 dark:text-red-400">
               {error}
             </div>
           )}
@@ -392,7 +392,7 @@ export function AddNotificationModal({ provider, onClose }: AddNotificationModal
             <div className={`p-3 rounded-lg flex items-center gap-2 ${
               testResult.success
                 ? 'bg-bambu-green/20 border border-bambu-green/50 text-bambu-green'
-                : 'bg-red-500/20 border border-red-500/50 text-red-400'
+                : 'bg-red-100 dark:bg-red-500/20 border border-red-300 dark:border-red-500/50 text-red-700 dark:text-red-400'
             }`}>
               {testResult.success ? (
                 <>