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/templates/login.html

@@ -0,0 +1,11 @@
+{% extends "base.html" %}
+{% block title %}로그인 · 습관 트래커{% endblock %}
+{% block content %}
+<div style="min-height: 70vh; display: flex; align-items: center; justify-content: center;">
+  <div class="card" style="width: 100%; max-width: 320px;">
+    <h1 style="text-align:center;">습관 트래커</h1>
+    <p style="text-align:center;">구글 계정으로 로그인하세요</p>
+    <a href="/auth/google/login" class="btn btn-primary btn-block">Google로 로그인</a>
+  </div>
+</div>
+{% endblock %}