fix: prevent native text selection on mobile long-press

iOS triggered both the app context menu and native text selection overlay
on long-press. Three-layer fix: CSS user-select:none on buttons/[role=button]/
[data-context-menu] elements; non-passive touchstart listener with conditional
preventDefault on context-menu targets; removeAllRanges() at timer fire to
clear any residual selection. Added data-context-menu to all mobile surfaces
that use onContextMenu handlers.

packages/web/src/components/chat/Message.tsx

@@ -224,6 +224,7 @@ export function Message({ message, isCompact, isFirstInGroup, previousMessageId
   const ownerId = spaces.find(s => s.id === currentSpaceId)?.ownerId;
 
   const getMemberDisplayColor = (userId: string) => {
+    if (isDmMessage) return { color: '#d8d8de' };
     const member = members.find(m => m.userId === userId);
     if (member?.roles && member.roles.length > 0) {
       const sorted = [...member.roles].sort((a, b) => b.position - a.position);
@@ -524,7 +525,7 @@ export function Message({ message, isCompact, isFirstInGroup, previousMessageId
   );
 
   return (
-    <div onContextMenu={handleContextMenu}>
+    <div data-context-menu onContextMenu={handleContextMenu}>
       {content}
     </div>
   );