fix: token tracking pipeline + premium usage dashboard redesign

Backend fixes:
- Fix totalTokens defaulting to 0 when API omits totalTokenCount (now computes prompt+completion)
- Fix streaming metadata extraction: unwrap response wrapper in Anthropic/Gemini handlers
- Fix Zod schemas: handle SQL SUM(null) with nullable().transform()
- Add is_estimated column migration to token_usage table

Frontend redesign:
- Rewrite Usage page with area charts (nivo/line), horizontal bar model ranking
- StatCard: add trend indicators (% vs previous period) and inline SVG sparklines
- Premium color palette, prompt/completion ratio bar, top models mini-list
- Live indicator with 15s auto-refresh

Design system migration:
- Standardize all components on Gemini Nexus tokens (rounded-xl, border-white/[0.06])
- Refine UI components, proxy tabs, cloud account list, provider groups

src/components/ui/switch.tsx

@@ -1,26 +1,31 @@
-import * as React from 'react';
-import * as SwitchPrimitive from '@radix-ui/react-switch';
-import { cn } from '@/lib/utils';
-
-const Switch = React.forwardRef<
-  React.ElementRef<typeof SwitchPrimitive.Root>,
-  React.ComponentPropsWithoutRef<typeof SwitchPrimitive.Root>
->(({ className, ...props }, ref) => (
-  <SwitchPrimitive.Root
-    className={cn(
-      'peer focus-visible:ring-ring focus-visible:ring-offset-background data-[state=checked]:bg-primary data-[state=unchecked]:bg-input inline-flex h-5 w-9 shrink-0 cursor-pointer items-center rounded-full border-2 border-transparent shadow-sm transition-colors focus-visible:ring-2 focus-visible:ring-offset-2 focus-visible:outline-none disabled:cursor-not-allowed disabled:opacity-50',
-      className,
-    )}
-    {...props}
-    ref={ref}
-  >
-    <SwitchPrimitive.Thumb
-      className={cn(
-        'bg-background pointer-events-none block h-4 w-4 rounded-full shadow-lg ring-0 transition-transform data-[state=checked]:translate-x-4 data-[state=unchecked]:translate-x-0',
-      )}
-    />
-  </SwitchPrimitive.Root>
-));
-Switch.displayName = SwitchPrimitive.Root.displayName;
-
-export { Switch };
+import * as React from 'react';
+import * as SwitchPrimitives from '@radix-ui/react-switch';
+
+import { cn } from '@/lib/utils';
+
+const Switch = React.forwardRef<
+  React.ElementRef<typeof SwitchPrimitives.Root>,
+  React.ComponentPropsWithoutRef<typeof SwitchPrimitives.Root>
+>(({ className, ...props }, ref) => (
+  <SwitchPrimitives.Root
+    className={cn(
+      'peer inline-flex h-5 w-9 shrink-0 cursor-pointer items-center rounded-full border border-transparent shadow-none transition-colors duration-200',
+      'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring/30 focus-visible:ring-offset-2 focus-visible:ring-offset-background',
+      'disabled:cursor-not-allowed disabled:opacity-50',
+      'data-[state=checked]:bg-accent data-[state=unchecked]:bg-white/[0.1]',
+      className,
+    )}
+    {...props}
+    ref={ref}
+  >
+    <SwitchPrimitives.Thumb
+      className={cn(
+        'pointer-events-none block h-4 w-4 rounded-full bg-white shadow-sm ring-0 transition-transform duration-200',
+        'data-[state=checked]:translate-x-[18px] data-[state=unchecked]:translate-x-0.5',
+      )}
+    />
+  </SwitchPrimitives.Root>
+));
+Switch.displayName = SwitchPrimitives.Root.displayName;
+
+export { Switch };