Restructure chat service, web routes, and add test suite

Split monolithic chat service into modular structure with Matrix client
support, extract web server into per-resource route modules, introduce
bootstrap/main-loop separation, and add comprehensive vitest coverage
across services, repositories, and utilities. Adds project docs and
CLAUDE.md agent instructions.

src/services/chat/index.ts

@@ -0,0 +1,24 @@
+export { ChatService } from './service.js';
+export type {
+  TokenRefresher,
+  UsernameResolver,
+  SyncStatus,
+  SyncProgress,
+  SyncPhase,
+  SyncProgressListener,
+} from './service.js';
+export type {
+  ActiveChat,
+  ChatMessage,
+  ChatMedia,
+  ChatCacheFile,
+  ScrapedChatMessage,
+  ScrapedRoom,
+} from './types.js';
+export { MatrixClient, MatrixAuthError } from './matrix/client.js';
+export type { MatrixCredentials } from './matrix/types.js';
+export {
+  extractMatrixCredentials,
+  loadCachedCredentials,
+} from './matrix/token-extractor.js';
+export { MatrixMediaDownloader } from './matrix/http-media-downloader.js';