feat: migrate Leptos frontend to Next.js 16 (React 19)

Complete migration from services/frontend.old/ (Leptos 0.7 WASM + Rust)
to services/frontend/ (Next.js 16 static export + TypeScript + Tailwind v4).

Summary:
- Port all shared types (message, guild, voice, media, dashboard, recording, ui)
- Build fetch-based API client covering all 30+ backend endpoints
- WebSocket client with auto-reconnect (exponential backoff, 20 attempts)
- React context provider for WS with typed event subscription (22 event types)
- Login page with localStorage auth + auto-redirect
- Dashboard layout with sidebar, header (WS status + theme toggle)
- Messages: feed, search, images tab, review tab, channel filter, detail modal
- Live: voice connection, music player, recordings, mic transmit, active speakers
- Dashboard: stats, user list, channel list, detail views
- Mascot chatbot with history + clear
- uiStateApi persistence for selected tab
- Add static export config, update deploy scripts and CI

services/frontend/src/lib/hooks/use-auth.tsx

@@ -0,0 +1,78 @@
+"use client";
+
+import {
+  createContext,
+  type ReactNode,
+  useCallback,
+  useContext,
+  useEffect,
+  useState,
+} from "react";
+import { login } from "@/lib/api";
+
+interface AuthContextValue {
+  authenticated: boolean;
+  loading: boolean;
+  login: (password: string) => Promise<boolean>;
+  logout: () => void;
+}
+
+const AuthContext = createContext<AuthContextValue | null>(null);
+
+export function AuthProvider({ children }: { children: ReactNode }) {
+  const [authenticated, setAuthenticated] = useState(false);
+  const [loading, setLoading] = useState(true);
+
+  useEffect(() => {
+    const password = localStorage.getItem("admin-password");
+    if (password) {
+      // Verify stored password still works
+      login(password)
+        .then((ok) => {
+          setAuthenticated(ok);
+          setLoading(false);
+        })
+        .catch(() => {
+          localStorage.removeItem("admin-password");
+          setLoading(false);
+        });
+    } else {
+      setLoading(false);
+    }
+  }, []);
+
+  const handleLogin = useCallback(async (password: string) => {
+    const ok = await login(password);
+    if (ok) {
+      localStorage.setItem("admin-password", password);
+      setAuthenticated(true);
+    }
+    return ok;
+  }, []);
+
+  const handleLogout = useCallback(() => {
+    localStorage.removeItem("admin-password");
+    setAuthenticated(false);
+  }, []);
+
+  return (
+    <AuthContext.Provider
+      value={{
+        authenticated,
+        loading,
+        login: handleLogin,
+        logout: handleLogout,
+      }}
+    >
+      {children}
+    </AuthContext.Provider>
+  );
+}
+
+export function useAuth(): AuthContextValue {
+  const ctx = useContext(AuthContext);
+  if (!ctx) {
+    throw new Error("useAuth must be used within an AuthProvider");
+  }
+  return ctx;
+}

services/frontend/src/lib/hooks/use-config.ts

@@ -0,0 +1,29 @@
+import { useState, useEffect } from "react";
+import { configApi } from "@/lib/api";
+
+export interface AppConfig {
+  monitorGuildId: string | null;
+  webserverPort?: number;
+  nodeEnv?: string;
+}
+
+export function useAppConfig() {
+  const [config, setConfig] = useState<AppConfig | null>(null);
+  const [loading, setLoading] = useState(true);
+
+  useEffect(() => {
+    configApi
+      .get()
+      .then((cfg) => {
+        setConfig({
+          monitorGuildId: cfg.monitor_guild_id ?? null,
+        });
+      })
+      .catch(() => {
+        // silent — config fetch is not critical
+      })
+      .finally(() => setLoading(false));
+  }, []);
+
+  return { config, loading };
+}