feat: create application DTOs

Add data-transfer-object interfaces for the application layer:
upload, file, bucket, S3, and auth domains.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/application/dto/s3.ts

@@ -0,0 +1,87 @@
+/**
+ * A single S3 object as it appears in listing results.
+ */
+export interface S3ObjectResponse {
+  /** The object key (full path within the bucket) */
+  key: string;
+  /** Stored file name (basename of the key) */
+  fileName: string;
+  /** MIME type of the stored object */
+  mimeType: string;
+  /** Object size in bytes */
+  sizeBytes: number;
+  /** High-level file category */
+  fileType: string;
+  /** SHA-256 hex digest of the object content */
+  etag: string | null;
+  /** ISO-8601 timestamp of last modification */
+  lastModified: string;
+  /** Public download URL */
+  downloadUrl: string;
+}
+
+/**
+ * Response payload for S3 ListObjectsV1 / ListObjectsV2.
+ */
+export interface S3ListObjectsResponse {
+  /** Array of object summaries */
+  objects: S3ObjectResponse[];
+  /** Common prefixes when a delimiter was used (e.g. "folder/" entries) */
+  prefixes: string[];
+  /** Whether more results are available */
+  isTruncated: boolean;
+  /** Token to pass as continuation-token to retrieve the next page */
+  nextContinuationToken: string | null;
+}
+
+/**
+ * Input for the copy-object operation (Web API v1).
+ */
+export interface S3CopyObjectInput {
+  /** Source object key within the same or source bucket */
+  sourceKey: string;
+  /** Destination bucket name; defaults to the source bucket when omitted */
+  destBucket?: string;
+  /** Destination object key */
+  destKey: string;
+}
+
+/**
+ * Response payload for the copy-object operation.
+ */
+export interface S3CopyObjectResponse {
+  /** Source object key that was copied */
+  sourceKey: string;
+  /** Destination object key */
+  destKey: string;
+  /** Destination bucket name */
+  destBucket: string;
+}
+
+/**
+ * Summary of a multipart upload in listing results.
+ */
+export interface S3MultipartUploadResponse {
+  /** The object key being uploaded */
+  key: string;
+  /** Upload identifier (nanoid) */
+  uploadId: string;
+  /** ISO-8601 timestamp when the upload was initiated */
+  initiatedAt: Date;
+  /** Identifier string of the upload initiator */
+  initiatedBy: string;
+}
+
+/**
+ * Summary of a single part within a multipart upload.
+ */
+export interface S3MultipartPartResponse {
+  /** 1-indexed part number */
+  partNumber: number;
+  /** ETag of the part content */
+  etag: string;
+  /** Part size in bytes */
+  sizeBytes: number;
+  /** ISO-8601 timestamp when the part was stored */
+  createdAt: Date;
+}