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/button.tsx

@@ -1,56 +1,59 @@
-import * as React from 'react';
-import { Slot } from '@radix-ui/react-slot';
-import { cva, type VariantProps } from 'class-variance-authority';
-
-import { cn } from '@/lib/utils';
-
-const buttonVariants = cva(
-  "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-md text-sm font-medium transition-all disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg:not([class*='size-'])]:size-4 shrink-0 [&_svg]:shrink-0 outline-none focus-visible:border-ring focus-visible:ring-ring/50 focus-visible:ring-[3px] aria-invalid:ring-destructive/20 dark:aria-invalid:ring-destructive/40 aria-invalid:border-destructive",
-  {
-    variants: {
-      variant: {
-        default: 'bg-primary text-primary-foreground shadow-none hover:bg-primary/90',
-        destructive:
-          'bg-destructive text-white shadow-none hover:bg-destructive/90 focus-visible:ring-destructive/20 dark:focus-visible:ring-destructive/40 dark:bg-destructive/60',
-        outline:
-          'border bg-background shadow-none hover:bg-accent hover:text-accent-foreground dark:bg-input/30 dark:border-input dark:hover:bg-input/50',
-        secondary: 'bg-secondary text-secondary-foreground shadow-none hover:bg-secondary/80',
-        ghost: 'hover:bg-accent hover:text-accent-foreground dark:hover:bg-accent/50',
-        link: 'text-primary underline-offset-4 hover:underline',
-      },
-      size: {
-        default: 'h-9 px-4 py-2 has-[>svg]:px-3',
-        sm: 'h-8 rounded-md gap-1.5 px-3 has-[>svg]:px-2.5',
-        lg: 'h-10 rounded-md px-6 has-[>svg]:px-4',
-        icon: 'size-9',
-      },
-    },
-    defaultVariants: {
-      variant: 'default',
-      size: 'default',
-    },
-  },
-);
-
-function Button({
-  className,
-  variant,
-  size,
-  asChild = false,
-  ...props
-}: React.ComponentProps<'button'> &
-  VariantProps<typeof buttonVariants> & {
-    asChild?: boolean;
-  }) {
-  const Comp = asChild ? Slot : 'button';
-
-  return (
-    <Comp
-      data-slot="button"
-      className={cn(buttonVariants({ variant, size, className }))}
-      {...props}
-    />
-  );
-}
-
-export { Button, buttonVariants };
+import * as React from 'react';
+import { Slot } from '@radix-ui/react-slot';
+import { cva, type VariantProps } from 'class-variance-authority';
+
+import { cn } from '@/lib/utils';
+
+const buttonVariants = cva(
+  "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-lg text-[13px] font-medium transition-all duration-200 disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg:not([class*='size-'])]:size-4 shrink-0 [&_svg]:shrink-0 outline-none focus-visible:ring-2 focus-visible:ring-ring/30 focus-visible:ring-offset-1 focus-visible:ring-offset-background",
+  {
+    variants: {
+      variant: {
+        default:
+          'bg-primary text-primary-foreground hover:bg-primary/90 active:scale-[0.98]',
+        destructive:
+          'bg-destructive/90 text-white hover:bg-destructive active:scale-[0.98] focus-visible:ring-destructive/30',
+        outline:
+          'border border-white/[0.08] bg-transparent hover:bg-white/[0.04] hover:border-white/[0.12] text-foreground',
+        secondary:
+          'bg-secondary text-secondary-foreground hover:bg-secondary/80 active:scale-[0.98]',
+        ghost:
+          'hover:bg-white/[0.06] text-muted-foreground hover:text-foreground',
+        link: 'text-accent underline-offset-4 hover:underline',
+      },
+      size: {
+        default: 'h-9 px-4 py-2',
+        sm: 'h-8 rounded-md gap-1.5 px-3 text-xs',
+        lg: 'h-10 rounded-lg px-6',
+        icon: 'size-8 rounded-lg',
+      },
+    },
+    defaultVariants: {
+      variant: 'default',
+      size: 'default',
+    },
+  },
+);
+
+function Button({
+  className,
+  variant,
+  size,
+  asChild = false,
+  ...props
+}: React.ComponentProps<'button'> &
+  VariantProps<typeof buttonVariants> & {
+    asChild?: boolean;
+  }) {
+  const Comp = asChild ? Slot : 'button';
+
+  return (
+    <Comp
+      data-slot="button"
+      className={cn(buttonVariants({ variant, size, className }))}
+      {...props}
+    />
+  );
+}
+
+export { Button, buttonVariants };