feat(m7): markdown notes with CRUD, preview, search, tests, e2e

- ProjectNoteRepository (CRUD, soft-delete, search title/body/tags,
  pinned-first ordering, index usage) + NoteService (membership permission,
  author/admin edit/delete, note_updated notification to other members,
  note_created/note_updated activity logs, pin/tags)
- APIs: notes list/create/detail/edit/delete
- Screens: notes list + NoteForm, note detail + NoteEditor + MarkdownBody
  preview, ProjectNav メモ link
- Unit tests (ProjectNoteRepository, NoteService) + e2e markdown-notes.spec

components/layout/ProjectNav.tsx

@@ -1,6 +1,7 @@
 const NAV_ITEMS = [
   { href: '', label: '概要' },
   { href: '/board', label: '掲示板' },
+  { href: '/notes', label: 'メモ' },
   { href: '/members', label: 'メンバー' },
   { href: '/activity', label: 'アクティビティ' },
   { href: '/settings', label: '設定' },
@@ -15,11 +16,12 @@ export function ProjectNav({
   active,
 }: {
   projectId: number;
-  active: 'overview' | 'board' | 'members' | 'activity' | 'settings';
+  active: 'overview' | 'board' | 'notes' | 'members' | 'activity' | 'settings';
 }) {
   const activeMap: Record<string, boolean> = {
     overview: active === 'overview',
     board: active === 'board',
+    notes: active === 'notes',
     members: active === 'members',
     activity: active === 'activity',
     settings: active === 'settings',