feat: v0.2.0 AriaEngine 自研存储引擎

- 新增 AriaEngine: LSM-Tree 页面式存储引擎，19 个模块，~3500 行 TS
  - page/: Slotted Page 格式 (header/slot/tuple/format) + CRC32
  - buffer/: Buffer Pool (LRU 缓存 + 驱逐策略)
  - index/: LSM-Tree (MemTable 红黑树 + SSTable + Bloom Filter + Merge Iterator)
  - wal/: WAL 日志 (二进制格式) + Checkpoint 管理
  - transaction/: MVCC 版本链 + 快照隔离
  - store/: IndexedDB / Memory 双后端抽象
  - compression/: LZ4 页面压缩

- 完整持久化: Schema 自动保存、SSTable 元数据管理、WAL 恢复
- 事务感知 CRUD: insert/update/delete 在事务中缓冲到 snapshot
- mode: 'aria' 激活自研引擎

- 新增 7 个测试文件，测试数 318 → 524，套件 20 → 27
  - aria-page.test.ts (32 tests): Page 格式单元测试
  - aria-index.test.ts (26 tests): Bloom Filter + MemTable
  - aria-sstable.test.ts (9 tests): SSTable Builder + Reader
  - aria-buffer.test.ts (25 tests): LRU + Eviction + Buffer Pool
  - aria-wal-mvcc.test.ts (22 tests): WAL 编解码 + MVCC 事务
  - aria-compress.test.ts (11 tests): LZ4 + Merge Iterator
  - aria.test.ts (80 tests): AriaEngine 集成 + 边界测试

- Bug 修复: LRUList size 跟踪、WAL 缓冲区越界、ColumnEncoding 导入
- 全面更新 README.md + site/ 站点文件 (index/docs/demo)

src/core.ts

@@ -11,6 +11,7 @@ import { DB_DEFAULTS, DatabaseError } from './constants';
 import { MemoryEngine } from './engine/memory';
 import { IndexedDBEngine } from './engine/indexeddb';
 import { OPFSEngine } from './engine/opfs';
+import { AriaEngine } from './engine/aria/index';
 import { HybridEngine } from './hybrid/index';
 import { Table } from './table/table';
 import { createSchema } from './table/schema';
@@ -258,6 +259,8 @@ export class MetonaSqlark {
         return new MemoryEngine();
       case 'disk':
         return diskEngine === 'opfs' ? new OPFSEngine() : new IndexedDBEngine();
+      case 'aria':
+        return new AriaEngine({ storageBackend: diskEngine === 'opfs' ? 'memory' : 'indexeddb' });
       case 'hybrid':
         return new HybridEngine(diskEngine);
       default: