Initial commit: habit tracker PWA with Google OAuth, push notifications

FastAPI + SQLAlchemy/Alembic + MariaDB backend with Jinja2/htmx/Alpine
server-rendered frontend. Multi-user via Google OAuth, daily habit
tracking, monthly/weekly history views, Web Push reminders via
APScheduler, and PWA support (manifest, service worker, offline caching).

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

app/template_utils.py

@@ -0,0 +1,25 @@
+from app.models.habit import ALL_WEEKDAYS_MASK
+from app.services.log_service import MILESTONE_STREAKS
+
+_DAY_LABELS = ["월", "화", "수", "목", "금", "토", "일"]
+
+
+def is_milestone_streak(streak: int) -> bool:
+    return streak in MILESTONE_STREAKS
+
+
+def weekday_label(mask: int) -> str:
+    if mask == ALL_WEEKDAYS_MASK:
+        return "매일"
+    days = [label for i, label in enumerate(_DAY_LABELS) if mask & (1 << i)]
+    return ", ".join(days) if days else "선택된 요일 없음"
+
+
+def heatmap_opacity(checked_count: int, scheduled_count: int) -> float:
+    """월별 캘린더 히트맵 셀의 배경 투명도(0~0.9)를 계산한다."""
+    if not scheduled_count:
+        return 0.0
+    ratio = checked_count / scheduled_count
+    if ratio <= 0:
+        return 0.0
+    return round(0.12 + ratio * 0.78, 2)