Add streamer dashboard stats; fix TTS overlap race properly

Dashboard now shows unique visitors (via sender link), total messages,
and unique senders per streamer, tracked via new viewer_visits/messages
tables.

The previous overlay TTS-overlap fix had a race: audio not having
arrived yet was treated the same as "no audio at all", letting the
queue advance before slow-to-synthesize audio (e.g. a long question)
ever started playing. Now "not arrived yet" is explicitly distinct
from "finished playing", with a grace-period fallback for genuine TTS
failures.

Also drop the hardcoded AI name from ai-prompt.txt since it's now
injected dynamically from the streamer's configured ai_name.

server.js

@@ -17,6 +17,9 @@ const {
   setViewerName,
   updateDisplayDuration,
   updateAiName,
+  recordVisit,
+  recordMessage,
+  getStreamerStats,
 } = require('./db');
 const { censorText } = require('./profanity');
 
@@ -127,6 +130,7 @@ app.get('/api/dashboard', requireAuth, (req, res) => {
     ttsVoice: streamer.tts_voice,
     displayDurationSeconds: streamer.display_duration_seconds,
     aiName: streamer.ai_name,
+    stats: getStreamerStats(streamer.id),
   });
 });
 
@@ -265,6 +269,14 @@ io.on('connection', (socket) => {
     } else {
       socket.join(`streamer-${streamer.id}`);
     }
+  } else if (role === 'sender' && connectedUser) {
+    // Only reached on the reconnect that happens right after login (see
+    // socket.disconnect()/connect() in send.js) — the initial anonymous
+    // connection has no session.user yet, so no visit is recorded for it.
+    const streamer = findStreamerBySenderToken(token);
+    if (streamer) {
+      recordVisit(streamer.id, connectedUser.id);
+    }
   }
 
   socket.on('disconnect', (reason) => {
@@ -294,6 +306,8 @@ io.on('connection', (socket) => {
         return;
       }
 
+      recordMessage(streamer.id, user.id);
+
       const rawMessage = text.trim().slice(0, 500);
       const message = censorText(rawMessage, '...');
       const speechMessage = censorText(rawMessage, 'бип');