feat(m8): SSE hub + realtime chat with mentions, tests, e2e

- SseHub (project-scoped client mgmt + broadcast, implements SseBroadcaster)
  with SSE-formatted payload; singleton getSseHub
- ChatRepository (message CRUD, soft-delete, search, pagination, project
  isolation) + ChatService (membership permission, send/edit/delete,
  @email mention -> mention notification, SSE broadcast of created/updated/deleted)
- SSE stream endpoint (ReadableStream + heartbeat + abort cleanup, membership)
- Chat message API routes (history/send/edit/delete)
- ChatWindow client (EventSource auto-reconnect, history fetch, realtime
  append/update/delete), chat page, ProjectNav チャット link
- SseEvent type now carries ChatMessage for chat events
- Unit (SseHub, ChatRepository, ChatService) + integration chat-sse-broadcast
  + e2e chat-sse (two contexts realtime)

services/ChatService.ts

@@ -0,0 +1,126 @@
+import {
+  ChatRepository,
+  type ListMessagesOptions,
+} from '@/repositories/ChatRepository';
+import type { Paginated } from '@/repositories/ChatRepository';
+import { ProjectMemberRepository } from '@/repositories/ProjectMemberRepository';
+import { UserRepository } from '@/repositories/UserRepository';
+import { NotificationService } from '@/services/NotificationService';
+import { SseHub } from '@/lib/sse/hub';
+import { ForbiddenError, NotFoundError, ValidationError } from '@/lib/errors';
+import type { ChatMessage } from '@/lib/types';
+
+const MENTION_RE = /@([^\s@]+@[^\s@]+\.[^\s@]+)/g;
+
+/**
+ * チャットの業務ロジックを担うService。
+ * 権限チェック、メッセージ送信/編集/削除、メンション通知、SSE配信を行う。
+ */
+export class ChatService {
+  constructor(
+    private readonly chatRepository: ChatRepository,
+    private readonly projectMemberRepository: ProjectMemberRepository,
+    private readonly userRepository: UserRepository,
+    private readonly notificationService: NotificationService,
+    private readonly sseHub: SseHub
+  ) {}
+
+  getHistory(
+    actorId: number,
+    projectId: number,
+    opts: ListMessagesOptions = {}
+  ): Paginated<ChatMessage> {
+    this.requireMember(projectId, actorId);
+    return this.chatRepository.findMessages(projectId, opts);
+  }
+
+  sendMessage(actorId: number, projectId: number, body: string): ChatMessage {
+    this.requireMember(projectId, actorId);
+    if (!body.trim()) {
+      throw new ValidationError('メッセージを入力してください', 'body');
+    }
+    const message = this.chatRepository.create({
+      projectId,
+      authorId: actorId,
+      body,
+    });
+
+    // メンション検出(@email) → 通知
+    const mentionedEmails = this.extractMentions(body);
+    for (const email of mentionedEmails) {
+      const mentioned = this.userRepository.findByEmail(email);
+      if (
+        mentioned &&
+        mentioned.id !== actorId &&
+        this.projectMemberRepository.isMember(projectId, mentioned.id)
+      ) {
+        this.notificationService.notifyOnEvent({
+          type: 'mention',
+          projectId,
+          title: `${email} にメンションされました`,
+          body: body.slice(0, 100),
+          mentionedUserId: mentioned.id,
+        });
+      }
+    }
+
+    this.sseHub.broadcast(projectId, {
+      type: 'chat.message.created',
+      data: { projectId, message },
+    });
+    return message;
+  }
+
+  editMessage(actorId: number, messageId: number, body: string): ChatMessage {
+    const message = this.chatRepository.findMessageById(messageId);
+    if (!message) throw new NotFoundError('ChatMessage', messageId);
+    this.requireMember(message.projectId, actorId);
+    if (message.authorId !== actorId) {
+      throw new ForbiddenError('自分のメッセージのみ編集できます');
+    }
+    if (!body.trim()) {
+      throw new ValidationError('メッセージを入力してください', 'body');
+    }
+    const updated = this.chatRepository.update(messageId, body);
+    if (!updated) throw new NotFoundError('ChatMessage', messageId);
+    this.sseHub.broadcast(message.projectId, {
+      type: 'chat.message.updated',
+      data: { projectId: message.projectId, message: updated },
+    });
+    return updated;
+  }
+
+  deleteMessage(actorId: number, messageId: number): void {
+    const message = this.chatRepository.findMessageById(messageId);
+    if (!message) throw new NotFoundError('ChatMessage', messageId);
+    this.requireMember(message.projectId, actorId);
+    const role = this.projectMemberRepository.getRole(
+      message.projectId,
+      actorId
+    );
+    if (message.authorId !== actorId && role !== 'admin') {
+      throw new ForbiddenError('投稿者または管理者のみ削除できます');
+    }
+    this.chatRepository.delete(messageId);
+    this.sseHub.broadcast(message.projectId, {
+      type: 'chat.message.deleted',
+      data: { projectId: message.projectId, id: messageId },
+    });
+  }
+
+  private requireMember(projectId: number, actorId: number): void {
+    if (!this.projectMemberRepository.isMember(projectId, actorId)) {
+      throw new ForbiddenError('プロジェクトに参加していません');
+    }
+  }
+
+  private extractMentions(body: string): string[] {
+    const emails = new Set<string>();
+    let match: RegExpExecArray | null;
+    MENTION_RE.lastIndex = 0;
+    while ((match = MENTION_RE.exec(body)) !== null) {
+      emails.add(match[1]);
+    }
+    return [...emails];
+  }
+}