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/pages/client/sidebar/HomeTab.tsx

@@ -99,6 +99,7 @@ export function HomeTab() {
         {(triggerRef) => (
           <SidebarAvatar
             as="button"
+            aria-label="Home"
             ref={triggerRef}
             outlined
             onClick={handleHomeClick}