fix(web): 点表情后光标不再跳出输入框，需要重新点击才能回车发送

点表情面板里的emoji这个操作本身没有做"点完之后把焦点还给输入框"
这件事——emoji按钮是个真实的<button>，点击后浏览器会把焦点停在
这个按钮上，导致输入框失焦，这时候按回车自然没反应（键盘事件根本
没送到输入框），要用户重新点一下输入框才能继续打字/发送。

参照"@"提及按钮已有的"点完之后把焦点和光标位置还给输入框"这套写法
（insertMentionTrigger/pickMention），给emoji选择也接上同一套逻辑，
并且改成插入到光标所在位置，而不是永远追加到文本末尾。

顺手把这三处（含原来的两处"@"相关逻辑）从 requestAnimationFrame
换成 setTimeout(fn, 0)：实测确认 requestAnimationFrame 在页面处于
后台/不可见状态时完全不会触发（浏览器的标准省电行为），而这个"点击
按钮后把焦点还给输入框"的操作没有理由依赖页面必须处于前台可见状态
才生效，setTimeout 不受这个限制。

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

web/src/features/messages/ConversationView.tsx

@@ -361,14 +361,18 @@ export function ConversationView() {
     setMentionTrigger(null);
     setEmojiOpen(false);
     // Matches insertMentionTrigger's own restore below -- without an explicit setSelectionRange
-    // (deferred a frame so the textarea's DOM value has actually updated to `inserted + after`
-    // first), the cursor doesn't reliably land right after the just-inserted "@Name ", making it
-    // awkward to keep typing; a bare focus() alone doesn't move the caret to a specific offset.
+    // (deferred so the textarea's DOM value has actually updated to `inserted + after` first), the
+    // cursor doesn't reliably land right after the just-inserted "@Name ", making it awkward to keep
+    // typing; a bare focus() alone doesn't move the caret to a specific offset. Deferred via
+    // setTimeout(0), not requestAnimationFrame -- rAF callbacks are paused outright while the tab is
+    // backgrounded/hidden (confirmed live: an rAF scheduled right after a click never fired at all
+    // in a hidden tab, a setTimeout(0) scheduled the same way fired normally), and this restore needs
+    // to run regardless of whether the tab happens to be foregrounded at that exact moment.
     const el = textareaRef.current;
-    requestAnimationFrame(() => {
+    setTimeout(() => {
       el?.focus();
       el?.setSelectionRange(inserted.length, inserted.length);
-    });
+    }, 0);
   };
 
   /** README §4.3's composer "@" toolbar icon -- same effect as typing '@' by hand, for groups. */
@@ -381,10 +385,10 @@ export function ConversationView() {
     setDraft(next);
     setMentionTrigger({ start: pos + insertion.length - 1, query: '' });
     setEmojiOpen(false);
-    requestAnimationFrame(() => {
+    setTimeout(() => {
       el?.focus();
       el?.setSelectionRange(pos + insertion.length, pos + insertion.length);
-    });
+    }, 0);
   };
 
   const handleKeyDown = (e: React.KeyboardEvent<HTMLTextAreaElement>) => {
@@ -717,8 +721,24 @@ export function ConversationView() {
                 <div className="absolute bottom-full left-0 z-20 mb-2">
                   <EmojiPanel
                     onPick={(emoji) => {
-                      setDraft(draft + emoji);
+                      // Same restore-focus-and-caret dance as insertMentionTrigger/pickMention above
+                      // -- clicking the emoji button moves DOM focus to it like any button click,
+                      // and without this the textarea stays unfocused until the user clicks back
+                      // into it (confirmed by a user report: Enter didn't send right after picking
+                      // an emoji because the textarea itself had lost focus). Inserts at the actual
+                      // caret position rather than always appending to the end, matching how a
+                      // mention insertion already behaves, so the two don't disagree about where
+                      // "here" is. setTimeout(0), not requestAnimationFrame -- see insertMentionTrigger's
+                      // own comment for why (rAF never fires at all while the tab is hidden).
+                      const el = textareaRef.current;
+                      const pos = el?.selectionStart ?? draft.length;
+                      const next = draft.slice(0, pos) + emoji + draft.slice(pos);
+                      setDraft(next);
                       setEmojiOpen(false);
+                      setTimeout(() => {
+                        el?.focus();
+                        el?.setSelectionRange(pos + emoji.length, pos + emoji.length);
+                      }, 0);
                     }}
                   />
                 </div>