feat(editor): add Tab key support for autocomplete selection

Tab now selects the currently highlighted item in all suggestion lists:
- EmojiSuggestionList (`:emoji` autocomplete)
- ProfileSuggestionList (`@mention` autocomplete)
- SlashCommandSuggestionList (`/command` autocomplete)

This is a common UX pattern that allows faster selection without
reaching for the Enter key.

https://claude.ai/code/session_01YWNAEhjLprna1iWcnQEr1o

src/components/editor/EmojiSuggestionList.tsx

@@ -58,7 +58,10 @@ export const EmojiSuggestionList = forwardRef<
         return true;
       }
 
-      if (event.key === "Enter" && !event.ctrlKey && !event.metaKey) {
+      if (
+        (event.key === "Enter" && !event.ctrlKey && !event.metaKey) ||
+        event.key === "Tab"
+      ) {
         if (items[selectedIndex]) {
           command(items[selectedIndex]);
         }

src/components/editor/ProfileSuggestionList.tsx

@@ -38,7 +38,10 @@ export const ProfileSuggestionList = forwardRef<
         return true;
       }
 
-      if (event.key === "Enter" && !event.ctrlKey && !event.metaKey) {
+      if (
+        (event.key === "Enter" && !event.ctrlKey && !event.metaKey) ||
+        event.key === "Tab"
+      ) {
         if (items[selectedIndex]) {
           command(items[selectedIndex]);
         }

src/components/editor/SlashCommandSuggestionList.tsx

@@ -38,7 +38,10 @@ export const SlashCommandSuggestionList = forwardRef<
         return true;
       }
 
-      if (event.key === "Enter" && !event.ctrlKey && !event.metaKey) {
+      if (
+        (event.key === "Enter" && !event.ctrlKey && !event.metaKey) ||
+        event.key === "Tab"
+      ) {
         if (items[selectedIndex]) {
           command(items[selectedIndex]);
         }