feat(frontend): Complete shadcn/ui migration with dark mode support and analytics updates.

- Convert all analytics components to use shadcn Card and semantic colors
- Update RawTransactionModal with proper shadcn styling and theme support
- Fix all remaining hardcoded colors to use CSS variables (bg-card, text-foreground, etc.)
- Ensure consistent theming across light/dark modes for all components
- Add custom tooltips with semantic colors for chart components

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/components/ui/theme-toggle.tsx

@@ -0,0 +1,52 @@
+import { Monitor, Moon, Sun } from "lucide-react";
+import { Button } from "./button";
+import { useTheme } from "../../contexts/ThemeContext";
+
+export function ThemeToggle() {
+  const { theme, setTheme } = useTheme();
+
+  const cycleTheme = () => {
+    if (theme === "light") {
+      setTheme("dark");
+    } else if (theme === "dark") {
+      setTheme("system");
+    } else {
+      setTheme("light");
+    }
+  };
+
+  const getIcon = () => {
+    switch (theme) {
+      case "light":
+        return <Sun className="h-4 w-4" />;
+      case "dark":
+        return <Moon className="h-4 w-4" />;
+      case "system":
+        return <Monitor className="h-4 w-4" />;
+    }
+  };
+
+  const getLabel = () => {
+    switch (theme) {
+      case "light":
+        return "Switch to dark mode";
+      case "dark":
+        return "Switch to system mode";
+      case "system":
+        return "Switch to light mode";
+    }
+  };
+
+  return (
+    <Button
+      variant="outline"
+      size="icon"
+      onClick={cycleTheme}
+      className="h-8 w-8"
+      title={getLabel()}
+    >
+      {getIcon()}
+      <span className="sr-only">{getLabel()}</span>
+    </Button>
+  );
+}