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/api/dashboard.ts

@@ -0,0 +1,38 @@
+import type {
+  DashboardChannelDetail,
+  DashboardStats,
+  DashboardUserDetail,
+  PaginatedChannels,
+  PaginatedUsers,
+} from "@/lib/types";
+import { api } from "./client";
+
+export const dashboardApi = {
+  getStats: () => api.get<DashboardStats>("/api/dashboard/stats"),
+
+  listUsers: (limit?: number, cursor?: string, search?: string) => {
+    const params = new URLSearchParams();
+    if (limit) params.set("limit", String(limit));
+    if (cursor) params.set("cursor", cursor);
+    if (search) params.set("search", search);
+    const qs = params.toString();
+    return api.get<PaginatedUsers>(`/api/dashboard/users${qs ? `?${qs}` : ""}`);
+  },
+
+  getUserDetail: (userId: string) =>
+    api.get<DashboardUserDetail>(`/api/dashboard/users/${userId}`),
+
+  listChannels: (limit?: number, search?: string, guildId?: string) => {
+    const params = new URLSearchParams();
+    if (limit) params.set("limit", String(limit));
+    if (search) params.set("search", search);
+    if (guildId) params.set("guild_id", guildId);
+    const qs = params.toString();
+    return api.get<PaginatedChannels>(
+      `/api/dashboard/channels${qs ? `?${qs}` : ""}`,
+    );
+  },
+
+  getChannelDetail: (channelId: string) =>
+    api.get<DashboardChannelDetail>(`/api/dashboard/channels/${channelId}`),
+};