Limit request sizes, answer 413, stop cleanly on SIGTERM

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UaC9HmtHMdRP8dAbN4wAKj

cal.js

@@ -306,7 +306,7 @@ function feed(req, res) {
 }
 
 // ---- HTTP API (called by server.js, behind the passkey gate)
-const readBody = req => new Promise((ok, no) => { const c = []; req.on('data', d => c.push(d)); req.on('end', () => ok(Buffer.concat(c).toString())); req.on('error', no); });
+const readBody = req => require('./body').readBody(req, 8e6);
 const json = (res, code, obj) => { res.writeHead(code, { 'content-type': 'application/json' }); res.end(JSON.stringify(obj)); };
 
 /** Every event in the window from all calendars (ICS links, iCloud, NE Hub, shared): { events, errors } */