fix: remove UploadBatcher crash window, make bot concurrency configurable, fix all test import paths

- Removed UploadBatcher (src/infrastructure/telegram/upload-batcher.ts + DI):
  pending uploads no longer lost on crash, files sent directly to Telegram
- Changed upload-controller to use Bun.file().stream() instead of createReadStream
- Made PER_BOT_CONCURRENCY configurable via TELEGRAM_BOT_CONCURRENCY env
- Fixed 18 test files with updated import paths and mock shapes
- Updated package.json test script: telegramQueue.test.ts → bot-pool.test.ts
- Build, lint, and test suite all pass

src/infrastructure/di.ts

@@ -19,7 +19,6 @@ import { DrizzleFileRepository } from './persistence/repositories/file-repositor
 import { DrizzleMultipartRepository } from './persistence/repositories/multipart-repository';
 import { botPool } from './telegram/bot-pool';
 import { ChunkedStorage } from './telegram/chunked-storage';
-import { UploadBatcher } from './telegram/upload-batcher';
 
 // ─── Repository Singletons ──────────────────────────────────────────
 
@@ -46,6 +45,3 @@ export const chunkedStorage = new ChunkedStorage(
   filePartRepository,
   telegramService,
 );
-
-/** Singleton UploadBatcher for batched small-file uploads. */
-export const uploadBatcher = new UploadBatcher(fileRepository, telegramService);