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/contexts/ThemeContext.tsx

@@ -0,0 +1,76 @@
+import React, { createContext, useContext, useEffect, useState } from "react";
+
+type Theme = "light" | "dark" | "system";
+
+interface ThemeContextType {
+  theme: Theme;
+  setTheme: (theme: Theme) => void;
+  actualTheme: "light" | "dark";
+}
+
+const ThemeContext = createContext<ThemeContextType | undefined>(undefined);
+
+export function ThemeProvider({ children }: { children: React.ReactNode }) {
+  const [theme, setTheme] = useState<Theme>(() => {
+    const stored = localStorage.getItem("theme") as Theme;
+    return stored || "system";
+  });
+
+  const [actualTheme, setActualTheme] = useState<"light" | "dark">("light");
+
+  useEffect(() => {
+    const root = window.document.documentElement;
+
+    const updateActualTheme = () => {
+      let resolvedTheme: "light" | "dark";
+
+      if (theme === "system") {
+        resolvedTheme = window.matchMedia("(prefers-color-scheme: dark)")
+          .matches
+          ? "dark"
+          : "light";
+      } else {
+        resolvedTheme = theme;
+      }
+
+      setActualTheme(resolvedTheme);
+
+      // Remove previous theme classes
+      root.classList.remove("light", "dark");
+
+      // Add resolved theme class
+      root.classList.add(resolvedTheme);
+    };
+
+    updateActualTheme();
+
+    // Listen for system theme changes
+    const mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
+    const handleChange = () => {
+      if (theme === "system") {
+        updateActualTheme();
+      }
+    };
+
+    mediaQuery.addEventListener("change", handleChange);
+
+    // Store theme preference
+    localStorage.setItem("theme", theme);
+
+    return () => mediaQuery.removeEventListener("change", handleChange);
+  }, [theme]);
+
+  return (
+    <ThemeContext.Provider value={{ theme, setTheme, actualTheme }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+}
+
+export function useTheme() {
+  const context = useContext(ThemeContext);
+  if (context === undefined) {
+    throw new Error("useTheme must be used within a ThemeProvider");
+  }
+  return context;
+}