add journaling feature: categories, tags, attachments, calendar, and multi-select emotions

Adds an 8th development stage that lets users keep a free-form journal alongside
habit tracking, reusing the existing Google OAuth/DB/PWA infrastructure instead
of a separate project. Users organize entries into custom categories, filter by
a month calendar with day-detail drill-down, attach photos/videos (served via an
authenticated route, never /static), tag entries, and pick multiple emotions per
entry from a curated 9-option set. Includes a global journal prompt bank for
lightweight guided journaling.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.env.example

@@ -20,3 +20,7 @@ GOOGLE_REDIRECT_URI=http://localhost:8000/auth/google/callback
 VAPID_PUBLIC_KEY=
 VAPID_PRIVATE_KEY=
 VAPID_SUBJECT=mailto:you@example.com
+
+# 저널 사진/영상 첨부 저장 경로(로컬 디스크)와 업로드 용량 제한(MB). 둘 다 기본값이 있어 생략 가능.
+# JOURNAL_MEDIA_ROOT=app/media/journal
+# JOURNAL_MAX_UPLOAD_MB=20