Let streamers set how long messages stay on screen

Adds display_duration_seconds to the streamers table (default 10s,
with an idempotent migration for existing rows), a dashboard control
to change it, and wires the value through to the overlay via the
display_message payload instead of a hardcoded 10s.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

server.js

@@ -13,6 +13,7 @@ const {
   getOrCreateStreamerByGoogle,
   getViewerName,
   setViewerName,
+  updateDisplayDuration,
 } = require('./db');
 
 const PORT = process.env.PORT || 3000;
@@ -116,9 +117,28 @@ app.get('/api/dashboard', requireAuth, (req, res) => {
     overlayUrl: `${origin}/overlay/${streamer.overlay_token}`,
     senderUrl: `${origin}/s/${streamer.sender_token}`,
     ttsVoice: streamer.tts_voice,
+    displayDurationSeconds: streamer.display_duration_seconds,
   });
 });
 
+app.post('/api/settings', requireAuth, (req, res) => {
+  const user = req.session.user;
+  const streamer = getOrCreateStreamerByGoogle({
+    googleId: user.id,
+    email: user.email,
+    name: user.name,
+    picture: user.picture,
+  });
+
+  const seconds = Number(req.body.displayDurationSeconds);
+  if (!Number.isInteger(seconds) || seconds < 1 || seconds > 120) {
+    return res.status(400).json({ error: 'displayDurationSeconds must be an integer between 1 and 120' });
+  }
+
+  updateDisplayDuration(streamer.id, seconds);
+  res.json({ displayDurationSeconds: seconds });
+});
+
 app.get('/api/viewer-name', requireAuth, (req, res) => {
   const streamer = findStreamerBySenderToken(req.query.token);
   if (!streamer) {
@@ -208,6 +228,7 @@ io.on('connection', (socket) => {
         text: message,
         from: displayName,
         at: Date.now(),
+        durationMs: (streamer.display_duration_seconds || 10) * 1000,
       });
 
       // Voice is generated after the fact so the text shows up immediately