Add self-hosted kids calendar app

Express + SQLite (node:sqlite, no native build step) family calendar:
parent accounts with household invites, per-child calendars with
save/duplicate/print, a token-gated read-only kiosk view for tablets,
and polling to keep parent and kiosk views in sync. Defaults to port 3007.

public/js/api.js

@@ -0,0 +1,29 @@
+const api = {
+  async request(method, path, body) {
+    const res = await fetch(path, {
+      method,
+      credentials: 'include',
+      headers: body !== undefined ? { 'Content-Type': 'application/json' } : undefined,
+      body: body !== undefined ? JSON.stringify(body) : undefined,
+    });
+
+    if (res.status === 204) return null;
+
+    let data = null;
+    const text = await res.text();
+    if (text) {
+      try { data = JSON.parse(text); } catch { data = null; }
+    }
+
+    if (!res.ok) {
+      const err = new Error((data && data.error) || `Request failed (${res.status})`);
+      err.status = res.status;
+      throw err;
+    }
+    return data;
+  },
+  get(path) { return this.request('GET', path); },
+  post(path, body) { return this.request('POST', path, body === undefined ? {} : body); },
+  patch(path, body) { return this.request('PATCH', path, body === undefined ? {} : body); },
+  del(path) { return this.request('DELETE', path); },
+};