feat: style Sonner toasts to match glassmorphic app theme

Drop richColors, apply dark glass background with subtle per-type
border tints (primary/success, red/error, amber/warning, blue/info).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/providers/Providers.tsx

@@ -25,7 +25,23 @@ export function Providers({ children }: { children: React.ReactNode }) {
         <SWRegistration />
         {children}
       </TooltipProvider>
-      <Toaster position="top-right" richColors />
+      <Toaster
+        theme="dark"
+        position="bottom-right"
+        toastOptions={{
+          classNames: {
+            toast:
+              '!bg-[#13131f] !border !border-white/8 !text-white/85 !rounded-xl !shadow-2xl !font-sans',
+            title: '!text-sm !font-medium !text-white/85',
+            description: '!text-xs !text-white/45',
+            icon: '!mt-px',
+            success: '!border-primary/25',
+            error: '!border-red-500/25',
+            warning: '!border-amber-400/25',
+            info: '!border-blue-400/25',
+          },
+        }}
+      />
     </QueryClientProvider>
   );
 }