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>

scripts/generate_vapid_keys.py

@@ -0,0 +1,19 @@
+"""Web Push용 VAPID 키쌍을 생성합니다. 출력값을 .env의 VAPID_PUBLIC_KEY/VAPID_PRIVATE_KEY에 붙여넣으세요.
+
+사용법: python scripts/generate_vapid_keys.py
+"""
+
+from cryptography.hazmat.primitives import serialization
+from py_vapid import Vapid02, b64urlencode
+
+if __name__ == "__main__":
+    vapid = Vapid02()
+    vapid.generate_keys()
+
+    private_raw = vapid.private_key.private_numbers().private_value.to_bytes(32, "big")
+    public_raw = vapid.public_key.public_bytes(
+        serialization.Encoding.X962, serialization.PublicFormat.UncompressedPoint
+    )
+
+    print("VAPID_PUBLIC_KEY=" + b64urlencode(public_raw))
+    print("VAPID_PRIVATE_KEY=" + b64urlencode(private_raw))