fix: bake standard tooltip styling into TooltipContent component

Added font-mono tabular-nums text-stat-value directly to the
TooltipContent base styles so every tooltip in the app inherits
the same look without per-instance wrappers. Removed the now-
redundant span from StackRow's RowTooltip.

frontend/src/components/sidebar/StackRow.tsx

@@ -38,7 +38,7 @@ function RowTooltip({ trigger, label }: { trigger: ReactNode; label: string }) {
       <Tooltip>
         <TooltipTrigger asChild>{trigger}</TooltipTrigger>
         <TooltipContent side="bottom" sideOffset={4} align="center">
-          <span className="font-mono text-xs tabular-nums text-stat-value">{label}</span>
+          {label}
         </TooltipContent>
       </Tooltip>
     </TooltipProvider>

frontend/src/components/sidebar/__tests__/StackRow.test.tsx

@@ -43,7 +43,7 @@ describe('StackRow', () => {
   });
 
   it('wraps the partial pill in a hover tooltip', () => {
-    const { container } = render(<StackRow {...base({ status: 'partial', running: 3, total: 5 })} />);
+    render(<StackRow {...base({ status: 'partial', running: 3, total: 5 })} />);
     const trigger = screen.getByText('PT');
     // Radix TooltipTrigger adds data-state to the wrapped element.
     expect(trigger.getAttribute('data-state')).toBe('closed');

frontend/src/components/ui/tooltip.tsx

@@ -19,7 +19,7 @@ const TooltipContent = React.forwardRef<
       ref={ref}
       sideOffset={sideOffset}
       className={cn(
-        'z-50 overflow-hidden rounded-md border border-glass-border bg-popover px-3 py-1.5 text-xs text-popover-foreground backdrop-blur-[10px] backdrop-saturate-[1.15]',
+        'z-50 overflow-hidden rounded-md border border-glass-border bg-popover px-3 py-1.5 font-mono text-xs tabular-nums text-stat-value backdrop-blur-[10px] backdrop-saturate-[1.15]',
         'origin-[--radix-tooltip-content-transform-origin]',
         'animate-in fade-in-0 zoom-in-95 duration-150',
         'data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=closed]:zoom-out-95',