Add attachments to comments

- CommentAttachment link table (comment <-> file) + migration
- fileIds in create/update comment; update replaces the whole set,
  synced in one transaction with the comment
- CommentDto.attachments; empty for deleted comments
- Soft delete drops attachments so GC can collect the files
- Max 10 files per comment, ordered by upload time (uuid v7)
- Registers comments as a file owner
- Rename CommentAuthorExpanderService -> CommentExpanderService
  (expands authors and files)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/modules/comment/application/mappers/comment-application.mapper.ts

@@ -1,15 +1,27 @@
 import { Comment } from '../../domain/entities/comment.entity.js';
 import { CommentDto } from '../dto/comment.dto.js';
 import { UserDto } from '../../../user/application/dto/user.dto.js';
+import { FileDto } from '../../../file/application/dto/file.dto.js';
 
 export class CommentApplicationMapper {
-  static toDto(comment: Comment, usersById: ReadonlyMap<string, UserDto>): CommentDto {
+  static toDto(
+    comment: Comment,
+    usersById: ReadonlyMap<string, UserDto>,
+    filesById: ReadonlyMap<string, FileDto> = new Map(),
+  ): CommentDto {
     return {
       id: comment.id as string,
       issueId: comment.issueId,
       authorId: comment.authorId,
       author: comment.authorId ? (usersById.get(comment.authorId) ?? null) : null,
       content: comment.isDeleted ? null : comment.content,
+      // Файл могли удалить между запросами — такое вложение просто не показываем
+      attachments: comment.isDeleted
+        ? []
+        : comment.fileIds.flatMap((fileId) => {
+            const file = filesById.get(fileId);
+            return file ? [file] : [];
+          }),
       editedAt: comment.editedAt,
       deletedAt: comment.deletedAt,
       createdAt: comment.createdAt,