feat: API analytics dashboard with i18n and theme support

Next.js full-stack analytics dashboard for new-api.
- Direct PostgreSQL readonly queries on logs table
- 5 pages: Dashboard, Rankings, Aggregation, Logs, Detail
- Dark/Light/System theme with CSS variables
- Chinese/English i18n (default Chinese)
- Recharts with dual Y-axis for input/output tokens
- Lucide icons + Motion animations
- Docker + docker-compose with external sinobridge network, port 8019

lib/theme.tsx

@@ -0,0 +1,74 @@
+"use client";
+
+import { createContext, useContext, useState, useEffect, type ReactNode } from "react";
+
+export type Theme = "light" | "dark" | "system";
+
+interface ThemeContextType {
+  theme: Theme;
+  setTheme: (t: Theme) => void;
+  resolved: "light" | "dark";
+}
+
+const ThemeContext = createContext<ThemeContextType>({
+  theme: "system",
+  setTheme: () => {},
+  resolved: "dark",
+});
+
+export function ThemeProvider({ children }: { children: ReactNode }) {
+  const [theme, setThemeState] = useState<Theme>("system");
+  const [resolved, setResolved] = useState<"light" | "dark">("dark");
+
+  useEffect(() => {
+    const saved = localStorage.getItem("theme") as Theme | null;
+    if (saved && ["light", "dark", "system"].includes(saved)) {
+      setThemeState(saved);
+    }
+  }, []);
+
+  useEffect(() => {
+    const resolve = () => {
+      if (theme === "system") {
+        return window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
+      }
+      return theme;
+    };
+
+    const r = resolve();
+    setResolved(r);
+
+    const root = document.documentElement;
+    root.classList.remove("light", "dark");
+    root.classList.add(r);
+    root.setAttribute("data-theme", r);
+
+    if (theme === "system") {
+      const mq = window.matchMedia("(prefers-color-scheme: dark)");
+      const handler = () => {
+        const nr = mq.matches ? "dark" : "light";
+        setResolved(nr);
+        root.classList.remove("light", "dark");
+        root.classList.add(nr);
+        root.setAttribute("data-theme", nr);
+      };
+      mq.addEventListener("change", handler);
+      return () => mq.removeEventListener("change", handler);
+    }
+  }, [theme]);
+
+  const setTheme = (t: Theme) => {
+    setThemeState(t);
+    localStorage.setItem("theme", t);
+  };
+
+  return (
+    <ThemeContext.Provider value={{ theme, setTheme, resolved }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+}
+
+export function useTheme() {
+  return useContext(ThemeContext);
+}