a11y: give every icon-only sidebar avatar button and the message sender avatar an accessible name (#185)

axe-core flagged 18 'button-name' criticals on the room view: the space
tabs, Home/Direct/Inbox/Search/Saved/Explore/Add Space/User Settings/
Unverified sidebar buttons, and each message's avatar button had no text
for screen readers. Labels mirror the existing tooltips; message avatars
read '<name>, open profile'. Room view now has zero button-name findings.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/room/message/Message.tsx

@@ -1015,6 +1015,7 @@ export const Message = React.memo(
                 size="300"
                 data-user-id={senderId}
                 onClick={onUserClick}
+                aria-label={`${senderDisplayName}, open profile`}
               >
                 <UserAvatar
                   userId={senderId}