Add KVStorageComposite, IndexedDB storage and SSE change streams

- Every KV storage emits change events (base class owns writeMany/removeMany/
  writeIfAbsent; implementations provide protected apply* methods)
- KVStorageHttpServer streams changes over SSE (GET /events) with a resumable
  history; KVStorageHttp.watch() subscribes and resumes via Last-Event-ID
- KVStorageIndexedDB for local persistence
- KVStorageComposite keeps replicas of a source in sync: local reads, resume
  instead of full sync, offline outbox replayed in order, echo tracking
- Values may contain bigint/Uint8Array (Extended JSON over the network)
- Vendor sse-session, event-emitter and extended-json (no runtime deps)
- Freeze child nodes so shadowed state on children fails loudly
- CI on Node 22, 24 and 26

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017Qxbkp4tA7G5SCWjzWuxmE

src/index.ts

@@ -2,6 +2,8 @@ export * from './kv-storage/base-kv-storage.js'
 export * from './kv-storage/kv-storage-in-memory.js'
 export * from './kv-storage/kv-storage-http.js'
 export * from './kv-storage/kv-storage-http-server.js'
+export * from './kv-storage/kv-storage-indexeddb.js'
+export * from './kv-storage/kv-storage-composite.js'
 export * from './event-storage/base-event-storage.js'
 export * from './event-storage/event-storage-kv.js'
 export * from './document-storage/base-document-storage.js'
@@ -12,6 +14,8 @@ export * from './utils/document-path.js'
 export * from './utils/document-query.js'
 export * from './utils/document-update.js'
 export * from './utils/errors.js'
+export * from './utils/event-emitter.js'
+export * from './utils/extended-json.js'
 export * from './utils/json.js'
 export * from './utils/keys.js'
 export * from './utils/schema.js'