feat: the assistant's send is a Telegram-like plane, its height pinned to the field's

internal/server/web/static/app.css

@@ -893,3 +893,8 @@ body:not(.touch) .ai-fab { cursor:grab; touch-action:none; }
 .ai-fab { transition:transform .22s ease, opacity .22s ease, box-shadow .2s ease, right .25s ease, bottom .25s ease; }
 .ai-fab.away { opacity:0; transform:scale(.5); pointer-events:none; }
 body.ai-dragging .ai-fab, body.ai-dragging .ai-box { transition:none; }
+/* The field and the send button: one height on every phone, the button
+   square whatever the text size. */
+.ai-form-in textarea { min-height:40px; }
+.ai-send { min-height:40px; max-height:40px; min-width:40px; max-width:40px; line-height:1; border-radius:10px; }
+.ai-form-in textarea { border-radius:10px; }