feat(profile): 'Active now' / 'Last active …' line from presence (#150)

One line under the handle in the user profile popover, from the presence the
SDK already receives (currently_active + last_active_ago): 'Active now',
'Active just now', 'Last active 12 min ago / 3 hours ago / yesterday / 5 days
ago / over a month ago'. Nothing is shown without presence data or for an
offline user with no timestamp (Hide Online Status users), so nothing new is
exposed; re-renders on the existing presence events, no polling. Wording
unit-tested; verified headless ('Active now' for an online member).

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

src/app/components/user-profile/UserRoomProfile.tsx

@@ -371,6 +371,7 @@ export function UserRoomProfile({ userId }: UserRoomProfileProps) {
               displayName={displayName}
               userId={userId}
               status={presence?.status}
+              presence={presence && presence.lastActiveTs !== 0 ? presence : undefined}
               pronouns={extProfile.pronouns}
               timezone={extProfile.timezone}
             />