feat: Phase 2 — auth, node/edge modals, API wiring

- Login page: full-screen dark, grid bg, JWT flow
- Auth store (Zustand) + API client (axios + interceptors)
- NodeModal: add/edit form (type, label, hostname, IP, check method)
- EdgeModal: link type picker + VLAN ID + label on connect
- App: auth gate, canvas load from API (fallback to demo), Ctrl+S save
- CanvasContainer: expose onConnect prop for edge modal flow

frontend/src/api/client.ts

@@ -0,0 +1,42 @@
+import axios from 'axios'
+import { useAuthStore } from '@/stores/authStore'
+
+export const api = axios.create({
+  baseURL: '/api/v1',
+})
+
+api.interceptors.request.use((config) => {
+  const token = useAuthStore.getState().token
+  if (token) config.headers.Authorization = `Bearer ${token}`
+  return config
+})
+
+api.interceptors.response.use(
+  (r) => r,
+  (err) => {
+    if (err.response?.status === 401) useAuthStore.getState().logout()
+    return Promise.reject(err)
+  }
+)
+
+export const authApi = {
+  login: (username: string, password: string) =>
+    api.post<{ access_token: string }>('/auth/login', { username, password }),
+}
+
+export const canvasApi = {
+  load: () => api.get('/canvas'),
+  save: (payload: { node_positions: { id: string; x: number; y: number }[]; viewport: object }) =>
+    api.post('/canvas/save', payload),
+}
+
+export const nodesApi = {
+  create: (data: object) => api.post('/nodes', data),
+  update: (id: string, data: object) => api.patch(`/nodes/${id}`, data),
+  delete: (id: string) => api.delete(`/nodes/${id}`),
+}
+
+export const edgesApi = {
+  create: (data: object) => api.post('/edges', data),
+  delete: (id: string) => api.delete(`/edges/${id}`),
+}