feat: implement Phase 2 (Go Agent) and Phase 3 (React Frontend MVP)

Phase 2 - Go Agent Core:
- gRPC client with exponential backoff reconnect logic
- Command executor (PowerShell/sh cross-platform)
- Proto stubs regenerated with module= option (correct output path)
- gRPC upgraded to v1.79.3 (BidiStreamingClient support)

Phase 3 - React Frontend MVP:
- Vite + React 18 + TypeScript setup with Tailwind CSS v4
- TanStack Query for data fetching, API client + TypeScript types
- Dashboard page: stats cards (agents/status/tickets) + sortable agents table
- Agent detail page: CPU/RAM charts (Recharts), disk usage, shell command executor
- Tickets page: CRUD with modals, filters, sortable table
- Dark mode with CSS custom properties

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Frontend/src/api/client.ts

@@ -0,0 +1,50 @@
+import type {
+  Agent,
+  AgentMetric,
+  TaskItem,
+  Ticket,
+  CreateTaskRequest,
+  CreateTicketRequest,
+  UpdateTicketRequest,
+} from './types'
+
+const BASE_URL = '/api/v1'
+
+async function request<T>(path: string, options?: RequestInit): Promise<T> {
+  const res = await fetch(`${BASE_URL}${path}`, {
+    headers: { 'Content-Type': 'application/json', ...options?.headers },
+    ...options,
+  })
+  if (!res.ok) {
+    const text = await res.text()
+    throw new Error(`HTTP ${res.status}: ${text}`)
+  }
+  if (res.status === 204) return undefined as T
+  return res.json() as Promise<T>
+}
+
+// Agents
+export const agentsApi = {
+  list: () => request<Agent[]>('/agents'),
+  get: (id: string) => request<Agent>(`/agents/${id}`),
+  getMetrics: (id: string, limit = 100) =>
+    request<AgentMetric[]>(`/agents/${id}/metrics?limit=${limit}`),
+}
+
+// Tasks
+export const tasksApi = {
+  create: (data: CreateTaskRequest) =>
+    request<TaskItem>('/tasks', { method: 'POST', body: JSON.stringify(data) }),
+  listForAgent: (agentId: string) =>
+    request<TaskItem[]>(`/tasks?agentId=${agentId}`),
+}
+
+// Tickets
+export const ticketsApi = {
+  list: () => request<Ticket[]>('/tickets'),
+  get: (id: number) => request<Ticket>(`/tickets/${id}`),
+  create: (data: CreateTicketRequest) =>
+    request<Ticket>('/tickets', { method: 'POST', body: JSON.stringify(data) }),
+  update: (id: number, data: UpdateTicketRequest) =>
+    request<Ticket>(`/tickets/${id}`, { method: 'PUT', body: JSON.stringify(data) }),
+}

Frontend/src/api/types.ts

@@ -0,0 +1,95 @@
+export type AgentStatus = 'Online' | 'Offline' | 'Degraded' | 'Pending'
+export type OsType = 'Windows' | 'Linux'
+export type TaskStatus = 'Pending' | 'InProgress' | 'Completed' | 'Failed' | 'Cancelled'
+export type TaskType = 'Shell' | 'InstallSoftware' | 'UninstallSoftware' | 'UpdateAgent' | 'NetworkScan'
+export type TicketStatus = 'Open' | 'InProgress' | 'Resolved' | 'Closed'
+export type TicketPriority = 'Low' | 'Medium' | 'High' | 'Critical'
+export type AlertSeverity = 'Info' | 'Warning' | 'Critical'
+
+export interface Agent {
+  id: string
+  hostname: string
+  osType: OsType
+  osVersion: string
+  ipAddress: string
+  macAddress: string
+  agentVersion: string
+  status: AgentStatus
+  lastSeen: string
+  tags: string[]
+  enrolledAt: string
+}
+
+export interface DiskInfo {
+  mountPoint: string
+  totalBytes: number
+  freeBytes: number
+  filesystem: string
+}
+
+export interface NetworkInterfaceInfo {
+  name: string
+  ipAddress: string
+  macAddress: string
+  bytesSent: number
+  bytesRecv: number
+}
+
+export interface SystemMetrics {
+  cpuUsagePercent: number
+  memoryUsagePercent: number
+  memoryTotalBytes: number
+  memoryAvailableBytes: number
+  disks: DiskInfo[]
+  networkInterfaces: NetworkInterfaceInfo[]
+  uptimeSeconds: number
+}
+
+export interface AgentMetric {
+  id: number
+  agentId: string
+  timestamp: string
+  metrics: SystemMetrics
+}
+
+export interface TaskItem {
+  id: string
+  agentId: string
+  type: TaskType
+  status: TaskStatus
+  payload: Record<string, unknown> | null
+  result: Record<string, unknown> | null
+  createdAt: string
+  completedAt: string | null
+}
+
+export interface Ticket {
+  id: number
+  title: string
+  description: string
+  status: TicketStatus
+  priority: TicketPriority
+  agentId: string | null
+  createdAt: string
+  updatedAt: string
+}
+
+export interface CreateTaskRequest {
+  agentId: string
+  type: TaskType
+  payload?: Record<string, unknown>
+}
+
+export interface CreateTicketRequest {
+  title: string
+  description: string
+  priority: TicketPriority
+  agentId?: string
+}
+
+export interface UpdateTicketRequest {
+  title?: string
+  description?: string
+  status?: TicketStatus
+  priority?: TicketPriority
+}