feat: add Rust backend — workspace with section executables

Cargo workspace with four crates:
- nixpanel-common: shared SectionRequest/SectionResponse types
- nixpanel-api: main Axum HTTP server (JWT auth, DB, routing)
- nixpanel-services: section binary for systemctl start/stop/restart
- nixpanel-sysinfo: section binary for CPU/RAM/disk/OS/version reads

nixpanel-api features:
- POST /api/auth/login — Argon2id verification, HS256 JWT
- GET  /api/dashboard  — real account counts + sysinfo + versions
- GET  /api/services   — live systemctl status via section binary
- POST /api/services/:name/:action — start/stop/restart
- GET  /api/accounts   — list from MariaDB
- POST /api/accounts   — create account + system user

Section binaries are UPX-compressed after build.
DB schema auto-migrated on first start; admin user seeded from
/opt/nixpanel/.admin_user + .admin_pass files.

Frontend changes:
- nixserver/src/api.ts + App.tsx wired to real API (JWT stored in
  localStorage, real data in dashboard/services/accounts)
- nixclient/src/api.ts added
- Both vite configs get /api proxy to localhost:4000 for dev
- install.sh updated to copy + compress all section binaries

nixserver/src/api.ts

@@ -0,0 +1,137 @@
+/* NixServer API client — all calls go to /api/ (proxied to Rust backend) */
+
+const BASE = '/api'
+
+/* ── Auth token ──────────────────────────────────────────────────────── */
+export function getToken(): string | null {
+  return localStorage.getItem('nixpanel_token')
+}
+export function setToken(t: string) {
+  localStorage.setItem('nixpanel_token', t)
+}
+export function clearToken() {
+  localStorage.removeItem('nixpanel_token')
+}
+export function isLoggedIn(): boolean {
+  return !!getToken()
+}
+
+/* ── Core fetch wrapper ──────────────────────────────────────────────── */
+async function apiFetch<T>(
+  path: string,
+  options: RequestInit = {}
+): Promise<T> {
+  const token = getToken()
+  const res = await fetch(`${BASE}${path}`, {
+    ...options,
+    headers: {
+      'Content-Type': 'application/json',
+      ...(token ? { Authorization: `Bearer ${token}` } : {}),
+      ...(options.headers ?? {}),
+    },
+  })
+  if (res.status === 401) {
+    clearToken()
+    window.location.reload()
+    throw new Error('Unauthorized')
+  }
+  if (!res.ok) {
+    const body = await res.json().catch(() => ({}))
+    throw new Error(body.error ?? `HTTP ${res.status}`)
+  }
+  return res.json()
+}
+
+/* ── Auth ────────────────────────────────────────────────────────────── */
+export interface LoginResult {
+  token: string
+  user: { id: number; username: string; role: string }
+}
+export async function login(username: string, password: string): Promise<LoginResult> {
+  const result = await apiFetch<LoginResult>('/auth/login', {
+    method: 'POST',
+    body: JSON.stringify({ username, password }),
+  })
+  setToken(result.token)
+  return result
+}
+
+/* ── Dashboard ───────────────────────────────────────────────────────── */
+export interface DashboardStats {
+  accounts: number
+  domains: number
+  databases: number
+  email_accounts: number
+}
+export interface SysInfo {
+  hostname: string
+  ip: string
+  os: string
+  kernel: string
+  uptime_sec: number
+  cpu_pct: number
+  ram_used_mb: number
+  ram_total_mb: number
+  disk_used_gb: number
+  disk_total_gb: number
+  load_avg: [number, number, number]
+}
+export interface Versions {
+  apache: string
+  php: string
+  mariadb: string
+  nixpanel: string
+}
+export interface DashboardData {
+  stats: DashboardStats
+  sysinfo: SysInfo | null
+  versions: Versions | null
+}
+export async function getDashboard(): Promise<DashboardData> {
+  return apiFetch('/dashboard')
+}
+
+/* ── Services ────────────────────────────────────────────────────────── */
+export interface ServiceInfo {
+  name: string
+  display: string
+  status: 'running' | 'stopped' | 'warning'
+  pid: number | null
+  uptime: string | null
+}
+export async function getServices(): Promise<ServiceInfo[]> {
+  return apiFetch('/services')
+}
+export async function serviceAction(
+  name: string,
+  action: 'start' | 'stop' | 'restart'
+): Promise<{ success: boolean; message: string }> {
+  return apiFetch(`/services/${name}/${action}`, { method: 'POST' })
+}
+
+/* ── Accounts ────────────────────────────────────────────────────────── */
+export interface Account {
+  id: number
+  username: string
+  domain: string
+  email: string
+  package_name: string
+  disk_quota_mb: number
+  bandwidth_mb: number
+  status: 'active' | 'suspended' | 'terminated'
+  created_at: string
+}
+export async function getAccounts(): Promise<Account[]> {
+  return apiFetch('/accounts')
+}
+export async function createAccount(data: {
+  username: string
+  domain: string
+  email: string
+  password: string
+  package_name?: string
+  disk_quota_mb?: number
+  bandwidth_mb?: number
+}): Promise<Account> {
+  return apiFetch('/accounts', { method: 'POST', body: JSON.stringify(data) })
+}