feat: 初始化 AI Code Diff Preview 插件项目

- 核心架构搭建：四层架构设计（触发层、隔离层、Diff引擎、UI层）
- 快照管理器：管理 Base/Suggest 双版本，隔离 AI 生成代码
- Diff 引擎：基于 Myers 算法计算差异，生成变更块
- 内联装饰器：红绿高亮显示删除/新增行
- CodeLens 提供器：提供 Accept/Reject 按钮
- 事务处理：Accept/Reject 原子化操作
- Claude Hooks 集成：支持 after_code_edit/after_write_file 事件
- 状态栏显示：实时显示变更状态
- 基础测试用例：7 个测试全部通过

技术栈：TypeScript + VSCode Extension API + diff 库 + esbuild

src/snapshot/snapshotManager.ts

@@ -0,0 +1,148 @@
+/**
+ * 快照管理器 - 管理文件的 Base/Suggest 双版本
+ */
+
+import { v4 as uuidv4 } from 'uuid';
+import { Snapshot, DiffChunk, ChunkStatus } from '../models/types';
+
+export class SnapshotManager {
+  private snapshots: Map<string, Snapshot> = new Map();
+  private filePathIndex: Map<string, string> = new Map(); // filePath -> snapshotId
+
+  /**
+   * 创建 Base 快照
+   */
+  createBaseSnapshot(filePath: string, baseContent: string): string {
+    const id = uuidv4();
+    const snapshot: Snapshot = {
+      id,
+      filePath,
+      baseContent,
+      suggestContent: '',
+      timestamp: Date.now(),
+      chunks: [],
+      status: 'active',
+    };
+
+    this.snapshots.set(id, snapshot);
+    this.filePathIndex.set(filePath, id);
+
+    return id;
+  }
+
+  /**
+   * 应用 AI 生成的 Patch
+   */
+  applyPatch(snapshotId: string, patch: string, chunks: DiffChunk[]): void {
+    const snapshot = this.snapshots.get(snapshotId);
+    if (!snapshot) {
+      throw new Error(`快照不存在: ${snapshotId}`);
+    }
+
+    snapshot.suggestContent = patch;
+    snapshot.chunks = chunks;
+  }
+
+  /**
+   * 获取快照
+   */
+  getSnapshot(snapshotId: string): Snapshot | undefined {
+    return this.snapshots.get(snapshotId);
+  }
+
+  /**
+   * 根据文件路径获取快照
+   */
+  getSnapshotByFilePath(filePath: string): Snapshot | undefined {
+    const snapshotId = this.filePathIndex.get(filePath);
+    if (!snapshotId) return undefined;
+    return this.snapshots.get(snapshotId);
+  }
+
+  /**
+   * 更新变更块状态
+   */
+  updateChunkStatus(snapshotId: string, chunkId: string, status: ChunkStatus): void {
+    const snapshot = this.snapshots.get(snapshotId);
+    if (!snapshot) return;
+
+    const chunk = snapshot.chunks.find(c => c.id === chunkId);
+    if (chunk) {
+      chunk.status = status;
+    }
+  }
+
+  /**
+   * 批量更新变更块状态
+   */
+  updateAllChunksStatus(snapshotId: string, status: ChunkStatus): void {
+    const snapshot = this.snapshots.get(snapshotId);
+    if (!snapshot) return;
+
+    snapshot.chunks.forEach(chunk => {
+      chunk.status = status;
+    });
+  }
+
+  /**
+   * 标记快照完成
+   */
+  completeSnapshot(snapshotId: string): void {
+    const snapshot = this.snapshots.get(snapshotId);
+    if (!snapshot) return;
+
+    snapshot.status = 'completed';
+    this.filePathIndex.delete(snapshot.filePath);
+  }
+
+  /**
+   * 取消快照
+   */
+  cancelSnapshot(snapshotId: string): void {
+    const snapshot = this.snapshots.get(snapshotId);
+    if (!snapshot) return;
+
+    snapshot.status = 'cancelled';
+    this.filePathIndex.delete(snapshot.filePath);
+  }
+
+  /**
+   * 删除快照
+   */
+  deleteSnapshot(snapshotId: string): void {
+    const snapshot = this.snapshots.get(snapshotId);
+    if (snapshot) {
+      this.filePathIndex.delete(snapshot.filePath);
+    }
+    this.snapshots.delete(snapshotId);
+  }
+
+  /**
+   * 获取所有活跃快照
+   */
+  getActiveSnapshots(): Snapshot[] {
+    return Array.from(this.snapshots.values()).filter(s => s.status === 'active');
+  }
+
+  /**
+   * 检查文件是否有活跃快照
+   */
+  hasActiveSnapshot(filePath: string): boolean {
+    const snapshotId = this.filePathIndex.get(filePath);
+    if (!snapshotId) return false;
+    const snapshot = this.snapshots.get(snapshotId);
+    return snapshot?.status === 'active';
+  }
+
+  /**
+   * 清理已完成或取消的快照
+   */
+  cleanup(): void {
+    for (const [id, snapshot] of this.snapshots.entries()) {
+      if (snapshot.status !== 'active') {
+        this.filePathIndex.delete(snapshot.filePath);
+        this.snapshots.delete(id);
+      }
+    }
+  }
+}