Add the Surface snapshot types to the TS contract authority

Why: U4 needs the frontend to render saved surfaces; the Go contract
(Core #25) gains its TypeScript mirror in the single authority so make
contracts regenerates the frontend and UI copies.

Evidence: Mirror regeneration and combined make test in the Dev
workspace after re-pinning.

Impact: Type-only additive change.

Refs: Core PR #25; Dev task feature/generative-ui-u4

ts/types.ts

@@ -354,3 +354,45 @@ export interface UploadInfo {
   artifactId: ID; filename: string; mime?: string; size: number;
   parsed?: ParsedDocument;
 }
+
+// ---- Generative UI Surface（提案 U2/U4；与 Go surface.go 同步）----
+
+export interface SurfaceCompat {
+  schemaVersion: number;
+  catalogVersion: string;
+  pluginVersion?: string;
+}
+
+export interface SurfaceIdentity {
+  surfaceId: ID;
+  owner: string;
+  projectId?: ID;
+  conversationId?: ID;
+  sourceRunId?: ID;
+  pluginId: string;
+}
+
+export interface SurfaceSpec {
+  title: string;
+  nodes: UINode[];
+}
+
+export interface SurfaceSnapshot {
+  identity: SurfaceIdentity;
+  compat: SurfaceCompat;
+  revision: number;
+  baseRevision?: number;
+  contextVersion?: string;
+  activationEpoch: number;
+  spec: SurfaceSpec;
+  semanticText?: string;
+}
+
+export interface SurfaceMeta {
+  surfaceId: ID;
+  title: string;
+  pluginId: string;
+  revision: number;
+  conversationId?: ID;
+  updatedAt: string;
+}