refactor: dedup dead code, shared utils, conditional headers helper

- Extract shared utils: asSafeChunkSize (validation.ts), S3 detection (s3-detection.ts)
- Remove dead _handleMaybeS3Root from index.ts and routes/index.ts
- Remove dead _asArray from file-controller.ts
- Consolidate maybeCompressChunk into shared compress.ts
- Extract checkConditionalHeaders helper, remove ~120 lines dupe in s3-controller
- Remove 500+ lines dead code from s3-object.ts (unused use cases + helpers)
- Delegate upload-file.ts chunked path to ChunkedStorage, remove dupe
- Fix broken dynamic import in file-controller.ts → proper DI
- Fix test/files.test.ts import path and mocks

[skip ci]

src/infrastructure/telegram/chunked-storage.ts

@@ -11,6 +11,7 @@ import { createGetObjectResponse, type ObjectPartSource } from '../../interfaces
 import type { RangeParseResult } from '../../interfaces/s3/range';
 import { type CompressionAlgorithm, maybeCompressChunk } from '../../shared/utils/compress';
 import { computeHash } from '../../shared/utils/file';
+import { asSafeChunkSize } from '../../shared/utils/validation';
 
 /**
  * Metadata about a single uploaded chunk (part) stored in Telegram.
@@ -70,20 +71,6 @@ export interface ChunkedFileInput {
   s3Key?: string | null;
 }
 
-/**
- * Validate and sanitise the Telegram chunk size.
- *
- * @param chunkSizeBytes - The desired chunk size in bytes.
- * @returns The validated chunk size.
- * @throws {Error} If the chunk size is not a safe positive integer.
- */
-const asSafeChunkSize = (chunkSizeBytes: number): number => {
-  if (!Number.isSafeInteger(chunkSizeBytes) || chunkSizeBytes <= 0) {
-    throw new Error('Invalid Telegram chunk size');
-  }
-  return chunkSizeBytes;
-};
-
 /**
  * Manages chunked storage of large files in Telegram.
  *