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/static/js/habit-reorder.js

@@ -0,0 +1,27 @@
+(function () {
+  function initSortable() {
+    var list = document.getElementById("habit-list");
+    if (!list || typeof Sortable === "undefined") return;
+
+    Sortable.create(list, {
+      handle: ".drag-handle",
+      animation: 150,
+      forceFallback: true, // iOS Safari는 네이티브 HTML5 D&D 터치 지원이 불안정해서 자체 포인터 시뮬레이션을 강제한다
+      fallbackTolerance: 3,
+      onEnd: function () {
+        var ids = Array.from(list.children)
+          .map(function (el) { return el.getAttribute("data-habit-id"); })
+          .filter(Boolean)
+          .map(Number);
+
+        fetch("/api/habits/reorder", {
+          method: "POST",
+          headers: { "Content-Type": "application/json" },
+          body: JSON.stringify({ habit_ids: ids }),
+        });
+      },
+    });
+  }
+
+  document.addEventListener("DOMContentLoaded", initSortable);
+})();