feat(m6): board with threads/comments, markdown, tests, e2e

- BoardRepository (thread/comment CRUD, soft-delete, search, pagination,
  pinned-first ordering) + BoardService (membership permission,
  author/admin edit/delete, comment->board_commented notification,
  board_posted/comment_added activity logs, category validation)
- APIs: threads list/create/detail/edit/delete, comments create/edit/delete
- MarkdownBody (react-markdown + remark-gfm + rehype-sanitize),
  ThreadForm, CommentForm, board list + thread detail screens, ProjectNav link
- Unit tests (BoardRepository, BoardService) + e2e board.spec

tests/e2e/board.spec.ts

@@ -0,0 +1,80 @@
+import { test, expect } from '@playwright/test';
+
+function unique(prefix: string): string {
+  return `${prefix}-${Date.now()}-${Math.floor(Math.random() * 1_000_000)}`;
+}
+
+async function setupOwner(page: import('@playwright/test').Page) {
+  const email = unique('owner') + '@example.com';
+  await page.goto('/login');
+  await page.getByRole('button', { name: '新規登録はこちら' }).click();
+  await page.getByLabel('表示名').fill('Owner');
+  await page.getByLabel('メールアドレス').fill(email);
+  await page.getByLabel('パスワード').fill('password123');
+  await page.getByRole('button', { name: '登録する' }).click();
+  await expect(page).toHaveURL(/\/dashboard/);
+
+  await page.getByLabel('プロジェクト名').fill(unique('Proj'));
+  await page.getByRole('button', { name: '新規プロジェクト' }).click();
+  await expect(page).toHaveURL(/\/projects\/\d+$/);
+  return Number(page.url().match(/\/projects\/(\d+)/)![1]);
+}
+
+test.describe('board', () => {
+  test('create thread, view detail, comment, and search', async ({ page }) => {
+    const projectId = await setupOwner(page);
+    const title = unique('Thread');
+
+    // スレッド作成(API)
+    const res = await page.request.post(
+      `/api/projects/${projectId}/board/threads`,
+      {
+        data: {
+          title,
+          bodyMd: '# Hello\n\nthis is **markdown**',
+          category: 'notice',
+        },
+      }
+    );
+    expect(res.ok()).toBeTruthy();
+    const { thread } = (await res.json()) as { thread: { id: number } };
+
+    // 一覧に表示される
+    await page.goto(`/projects/${projectId}/board`);
+    await expect(
+      page.getByRole('link', { name: new RegExp(title) })
+    ).toBeVisible();
+
+    // 詳細: Markdown本文が表示される
+    await page.goto(`/projects/${projectId}/board/${thread.id}`);
+    await expect(
+      page.getByRole('heading', { name: 'Hello', level: 1 })
+    ).toBeVisible();
+    await expect(page.getByText('markdown')).toBeVisible();
+
+    // コメント追加(API) → 詳細に表示される
+    const commentRes = await page.request.post(
+      `/api/projects/${projectId}/board/threads/${thread.id}/comments`,
+      { data: { bodyMd: 'first comment' } }
+    );
+    expect(commentRes.ok()).toBeTruthy();
+    await page.reload();
+    await expect(page.getByText('first comment')).toBeVisible();
+
+    // 検索: 別スレッドを作成し、q で絞り込める
+    const otherTitle = unique('ZZZ');
+    await page.request.post(`/api/projects/${projectId}/board/threads`, {
+      data: { title: otherTitle, bodyMd: 'body', category: 'question' },
+    });
+    await page.goto(
+      `/projects/${projectId}/board?q=${encodeURIComponent(otherTitle)}`
+    );
+    await expect(
+      page.getByRole('link', { name: new RegExp(otherTitle) })
+    ).toBeVisible();
+    // 前のスレッドは検索結果に含まれない
+    await expect(
+      page.getByRole('link', { name: new RegExp(title) })
+    ).toHaveCount(0);
+  });
+});