feat: Holistic app consistency improvements

Fixes:
- Chart hover dot now uses DOM element instead of SVG circle (no more squished dots)
- Chart hover line uses proper stroke-dasharray
- Tooltip positioning improved

New Components:
- Shimmer.tsx: Unified shimmer component for loading/locked states
- 404 Page: Professional not-found page with navigation options

Consistency improvements identified for future:
- All pages now use consistent Header/Footer
- Trend colors standardized (orange=up, green=down)
- Typography system follows design tokens

frontend/src/app/not-found.tsx

@@ -0,0 +1,68 @@
+'use client'
+
+import Link from 'next/link'
+import { Header } from '@/components/Header'
+import { Footer } from '@/components/Footer'
+import { Home, Search, ArrowLeft } from 'lucide-react'
+
+export default function NotFound() {
+  return (
+    <div className="min-h-screen bg-background relative flex flex-col">
+      {/* Ambient glow */}
+      <div className="fixed inset-0 pointer-events-none">
+        <div className="absolute top-1/4 left-1/2 -translate-x-1/2 w-[500px] h-[400px] bg-accent/[0.02] rounded-full blur-3xl" />
+      </div>
+
+      <Header />
+
+      <main className="relative flex-1 flex items-center justify-center px-4 sm:px-6 py-20">
+        <div className="text-center max-w-md">
+          {/* 404 Number */}
+          <div className="mb-8">
+            <span className="font-mono text-[8rem] sm:text-[10rem] leading-none font-bold text-foreground/[0.06] select-none">
+              404
+            </span>
+          </div>
+
+          {/* Content */}
+          <h1 className="font-display text-[2rem] sm:text-[2.5rem] leading-[1.1] tracking-[-0.03em] text-foreground mb-4">
+            Page not found
+          </h1>
+          <p className="text-body text-foreground-muted mb-10">
+            The page you're looking for doesn't exist or has been moved.
+          </p>
+
+          {/* Actions */}
+          <div className="flex flex-col sm:flex-row items-center justify-center gap-3">
+            <Link
+              href="/"
+              className="flex items-center justify-center gap-2 w-full sm:w-auto px-6 py-3 bg-foreground text-background font-medium rounded-xl hover:bg-foreground/90 transition-all"
+            >
+              <Home className="w-4 h-4" />
+              Go Home
+            </Link>
+            <Link
+              href="/tld-pricing"
+              className="flex items-center justify-center gap-2 w-full sm:w-auto px-6 py-3 bg-background-secondary border border-border text-foreground font-medium rounded-xl hover:border-border-hover hover:bg-background-secondary/80 transition-all"
+            >
+              <Search className="w-4 h-4" />
+              Browse TLDs
+            </Link>
+          </div>
+
+          {/* Back Link */}
+          <button
+            onClick={() => window.history.back()}
+            className="mt-8 inline-flex items-center gap-2 text-body-sm text-foreground-muted hover:text-foreground transition-colors"
+          >
+            <ArrowLeft className="w-4 h-4" />
+            Go back
+          </button>
+        </div>
+      </main>
+
+      <Footer />
+    </div>
+  )
+}
+

frontend/src/app/tld-pricing/[tld]/page.tsx

@@ -235,36 +235,40 @@ function PriceChart({
           filter="url(#glow)"
         />
 
-        {/* Hover point */}
+        {/* Hover indicator */}
         {hoveredIndex !== null && (
-          <>
+          <g>
             <line
               x1={points[hoveredIndex].x}
               y1="0"
               x2={points[hoveredIndex].x}
               y2="100"
               stroke="rgb(0, 212, 170)"
-              strokeWidth="0.2"
-              strokeDasharray="2 2"
+              strokeWidth="1"
+              strokeDasharray="4 4"
               vectorEffect="non-scaling-stroke"
-              opacity="0.5"
+              opacity="0.3"
             />
-            <circle
-              cx={points[hoveredIndex].x}
-              cy={points[hoveredIndex].y}
-              r="1"
-              fill="rgb(0, 212, 170)"
-              vectorEffect="non-scaling-stroke"
-            />
-          </>
+          </g>
         )}
       </svg>
 
+      {/* Hover dot */}
+      {hoveredIndex !== null && containerRef.current && (
+        <div
+          className="absolute w-3 h-3 bg-accent rounded-full border-2 border-background shadow-lg pointer-events-none transform -translate-x-1/2 -translate-y-1/2 transition-all duration-75"
+          style={{ 
+            left: `${(points[hoveredIndex].x / 100) * containerRef.current.offsetWidth}px`, 
+            top: `${(points[hoveredIndex].y / 100) * containerRef.current.offsetHeight}px` 
+          }}
+        />
+      )}
+
       {/* Tooltip */}
       {hoveredIndex !== null && (
         <div
-          className="absolute z-20 px-3 py-2 bg-background border border-border rounded-lg shadow-xl pointer-events-none transform -translate-x-1/2 -translate-y-full"
-          style={{ left: tooltipPos.x, top: tooltipPos.y - 10 }}
+          className="absolute z-20 px-3 py-2 bg-background border border-border rounded-lg shadow-xl pointer-events-none transform -translate-x-1/2"
+          style={{ left: tooltipPos.x, top: Math.max(tooltipPos.y - 60, 10) }}
         >
           <p className="text-ui-sm font-medium text-foreground tabular-nums">
             ${data[hoveredIndex].price.toFixed(2)}

frontend/src/components/Shimmer.tsx

@@ -0,0 +1,46 @@
+'use client'
+
+import clsx from 'clsx'
+
+interface ShimmerProps {
+  className?: string
+  variant?: 'default' | 'text' | 'card'
+}
+
+/**
+ * Unified Shimmer component for loading/locked states
+ * Use throughout the app for consistent loading UI
+ */
+export function Shimmer({ className, variant = 'default' }: ShimmerProps) {
+  return (
+    <div className={clsx(
+      "relative overflow-hidden rounded",
+      variant === 'default' && "bg-foreground/[0.06]",
+      variant === 'text' && "bg-foreground/[0.04]",
+      variant === 'card' && "bg-foreground/[0.03]",
+      className
+    )}>
+      <div 
+        className="absolute inset-0 -translate-x-full bg-gradient-to-r from-transparent via-foreground/[0.08] to-transparent"
+        style={{
+          animation: 'shimmer 2s infinite',
+        }}
+      />
+    </div>
+  )
+}
+
+/**
+ * Shimmer block for price/data placeholders when user is not authenticated
+ */
+export function ShimmerBlock({ className }: { className?: string }) {
+  return <Shimmer className={className} variant="default" />
+}
+
+/**
+ * Shimmer text for inline text placeholders
+ */
+export function ShimmerText({ className }: { className?: string }) {
+  return <Shimmer className={clsx("h-4", className)} variant="text" />
+}
+