Let viewers set a per-streamer display name

Viewers can type a custom name shown to the streamer instead of
their Google account name. It's saved per (streamer, viewer) pair
in SQLite and pre-filled on future visits to the same send link.

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

public/send.html

@@ -38,6 +38,19 @@
     color: #888;
     font-size: 14px;
   }
+  label {
+    display: block;
+    font-size: 13px;
+    color: #666;
+    margin-bottom: 4px;
+  }
+  #display-name {
+    width: 100%;
+    font-size: 16px;
+    padding: 8px 10px;
+    box-sizing: border-box;
+    margin-bottom: 16px;
+  }
   textarea {
     width: 100%;
     height: 100px;
@@ -77,6 +90,9 @@
     <span id="logout">выйти</span>
   </div>
 
+  <label for="display-name">Ваше имя (покажется стримеру вместо имени из Google)</label>
+  <input id="display-name" type="text" maxlength="60" placeholder="Имя..." />
+
   <textarea id="message" placeholder="Текст для стрима..." maxlength="500"></textarea>
   <br />
   <button id="send">Отправить</button>