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.

src/middleware/resolveKiosk.js

@@ -0,0 +1,15 @@
+const db = require('../db');
+
+const getChildByTokenStmt = db.prepare('SELECT * FROM children WHERE kiosk_token = ?');
+
+function resolveKiosk(req, res, next) {
+  if (typeof req.params.token !== 'string' || !req.params.token) {
+    return res.status(404).json({ error: 'Invalid kiosk link' });
+  }
+  const child = getChildByTokenStmt.get(req.params.token);
+  if (!child) return res.status(404).json({ error: 'Invalid kiosk link' });
+  req.child = child;
+  next();
+}
+
+module.exports = resolveKiosk;