merge: 集成共享 Agent Browser 调试能力

需求：将 Agent Browser 独立功能提交合并到包含 AI 设计 Workspace 的最新主线。

实现：保留双方模块初始化、Host API 路由和 README 产品说明。

# Conflicts:
#	electron/api/context.ts

shared/agent-browser.ts

@@ -0,0 +1,107 @@
+export type AgentBrowserState =
+  | 'closed'
+  | 'opening'
+  | 'attaching'
+  | 'attached'
+  | 'suspended_devtools'
+  | 'detached_fault'
+  | 'crashed'
+  | 'closing';
+
+export interface AgentBrowserBounds {
+  x: number;
+  y: number;
+  width: number;
+  height: number;
+}
+
+export interface AgentBrowserPayloadRef {
+  kind: 'payload';
+  handle: string;
+  byteLength: number;
+  contentType: 'application/json' | 'text/plain' | 'application/octet-stream';
+  expiresAt: string;
+}
+
+export interface AgentBrowserSnapshot {
+  browserId: string | null;
+  projectId: string | null;
+  projectPath: string | null;
+  state: AgentBrowserState;
+  generation: number;
+  url: string;
+  title: string;
+  visible: boolean;
+  bounds: AgentBrowserBounds | null;
+  canGoBack: boolean;
+  canGoForward: boolean;
+  eventCursor: number;
+  error?: {
+    code: AgentBrowserErrorCode;
+    message: string;
+  };
+}
+
+export interface AgentBrowserCdpEvent {
+  sequence: number;
+  generation: number;
+  timestamp: number;
+  method: string;
+  params?: unknown;
+  payload?: AgentBrowserPayloadRef;
+  sessionRef?: string;
+}
+
+export interface AgentBrowserCdpEventPage {
+  events: AgentBrowserCdpEvent[];
+  nextCursor: number;
+  hasMore: boolean;
+  gap?: {
+    reason: 'evicted' | 'debugger-detached' | 'view-recreated';
+    oldestAvailable: number;
+  };
+}
+
+export type AgentBrowserCdpResult =
+  | { kind: 'inline'; value: unknown }
+  | AgentBrowserPayloadRef;
+
+export interface AgentBrowserPayloadChunk {
+  handle: string;
+  offset: number;
+  nextOffset: number;
+  byteLength: number;
+  contentType: AgentBrowserPayloadRef['contentType'];
+  data: string;
+  encoding: 'utf8' | 'base64';
+  done: boolean;
+}
+
+export type AgentBrowserErrorCode =
+  | 'PROJECT_NOT_ACTIVE'
+  | 'PROJECT_MISMATCH'
+  | 'BROWSER_NOT_OPEN'
+  | 'VIEWPORT_NOT_READY'
+  | 'DEBUGGER_BUSY'
+  | 'ATTACH_FAILED'
+  | 'DEVTOOLS_CONFLICT'
+  | 'CDP_METHOD_BLOCKED'
+  | 'TARGET_DENIED'
+  | 'CDP_TIMEOUT'
+  | 'CDP_PROTOCOL_ERROR'
+  | 'CURSOR_EXPIRED'
+  | 'PAYLOAD_NOT_FOUND'
+  | 'PAYLOAD_TOO_LARGE'
+  | 'TARGET_GONE'
+  | 'RENDERER_CRASHED'
+  | 'INVALID_URL'
+  | 'INVALID_REQUEST'
+  | 'CLOSED';
+
+export interface AgentBrowserFaultShape {
+  code: AgentBrowserErrorCode;
+  message: string;
+  retryable: boolean;
+  generation?: number;
+  outcome?: 'unknown';
+}