Fix two light-mode rendering bugs flagged by full audit

Toast.svelte: hardcoded bg-[#222228] kept the toast dark in light mode
while text-fg-primary flipped to dark text, producing invisible labels.
Replaced with bg-bg-elevated so background and text invert together.

WallpaperEditor.svelte: "Loading image..." used text-fg-dimmed over a
fixed bg-black/40 scrim; the text flipped to dark in light mode while
the scrim stayed dark. Switched to text-white/80 per the CLAUDE.md rule
("never theme tokens on a black scrim").

Audit of ~50 components found no other real light-mode regressions.

Author: bjarneo

frontend/src/lib/components/shared/Toast.svelte

@@ -21,7 +21,7 @@
 
 {#if visible}
     <div
-        class="border-border text-fg-primary fixed bottom-14 left-1/2 z-[100] flex -translate-x-1/2 items-center gap-3 border bg-[#222228] px-4 py-2 text-[12px] shadow-lg"
+        class="border-border bg-bg-elevated text-fg-primary fixed bottom-14 left-1/2 z-[100] flex -translate-x-1/2 items-center gap-3 border px-4 py-2 text-[12px] shadow-lg"
         style="animation: toast-in 150ms ease-out"
         role="status"
         aria-live="polite"

frontend/src/lib/components/wallpaper-editor/WallpaperEditor.svelte

@@ -527,7 +527,7 @@
                             <div
                                 class="absolute inset-0 flex items-center justify-center bg-black/40"
                             >
-                                <span class="text-fg-dimmed text-[12px]"
+                                <span class="text-[12px] text-white/80"
                                     >Loading image...</span
                                 >
                             </div>