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/tooltip.tsx

@@ -1,28 +1,31 @@
-import * as React from 'react';
-import * as TooltipPrimitive from '@radix-ui/react-tooltip';
-
-import { cn } from '@/lib/utils';
-
-const TooltipProvider = TooltipPrimitive.Provider;
-
-const Tooltip = TooltipPrimitive.Root;
-
-const TooltipTrigger = TooltipPrimitive.Trigger;
-
-const TooltipContent = React.forwardRef<
-  React.ElementRef<typeof TooltipPrimitive.Content>,
-  React.ComponentPropsWithoutRef<typeof TooltipPrimitive.Content>
->(({ className, sideOffset = 4, ...props }, ref) => (
-  <TooltipPrimitive.Content
-    ref={ref}
-    sideOffset={sideOffset}
-    className={cn(
-      'bg-popover text-popover-foreground animate-in fade-in-0 zoom-in-95 data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=closed]:zoom-out-95 data-[side=bottom]:slide-in-from-top-2 data-[side=left]:slide-in-from-right-2 data-[side=right]:slide-in-from-left-2 data-[side=top]:slide-in-from-bottom-2 z-50 origin-[--radix-tooltip-content-transform-origin] overflow-hidden rounded-md border px-3 py-1.5 text-sm shadow-md',
-      className,
-    )}
-    {...props}
-  />
-));
-TooltipContent.displayName = TooltipPrimitive.Content.displayName;
-
-export { Tooltip, TooltipTrigger, TooltipContent, TooltipProvider };
+import * as React from 'react';
+import * as TooltipPrimitive from '@radix-ui/react-tooltip';
+
+import { cn } from '@/lib/utils';
+
+const TooltipProvider = TooltipPrimitive.Provider;
+
+const Tooltip = TooltipPrimitive.Root;
+
+const TooltipTrigger = TooltipPrimitive.Trigger;
+
+const TooltipContent = React.forwardRef<
+  React.ElementRef<typeof TooltipPrimitive.Content>,
+  React.ComponentPropsWithoutRef<typeof TooltipPrimitive.Content>
+>(({ className, sideOffset = 4, ...props }, ref) => (
+  <TooltipPrimitive.Content
+    ref={ref}
+    sideOffset={sideOffset}
+    className={cn(
+      'z-50 overflow-hidden rounded-lg border border-white/[0.08] bg-popover px-3 py-1.5 text-xs text-popover-foreground shadow-lg shadow-black/20',
+      'animate-in fade-in-0 zoom-in-95',
+      'data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=closed]:zoom-out-95',
+      'data-[side=bottom]:slide-in-from-top-2 data-[side=left]:slide-in-from-right-2 data-[side=right]:slide-in-from-left-2 data-[side=top]:slide-in-from-bottom-2',
+      className,
+    )}
+    {...props}
+  />
+));
+TooltipContent.displayName = TooltipPrimitive.Content.displayName;
+
+export { Tooltip, TooltipTrigger, TooltipContent, TooltipProvider };