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/UnverifiedTab.tsx

@@ -54,6 +54,11 @@ function UnverifiedIndicator() {
               <SidebarAvatar
                 className={unverified ? css.UnverifiedAvatar : css.UnverifiedOtherAvatar}
                 as="button"
+                aria-label={
+                  unverified
+                    ? 'Unverified device — open settings'
+                    : 'Other unverified devices — open settings'
+                }
                 ref={triggerRef}
                 outlined
                 onClick={() => setSettings(true)}