fix(lobby): keep the spaces around the score separator

Svelte trims leading/trailing whitespace inside an element, so the literal
`<span class="sep"> : </span>` rendered as a bare ":" ("123:123"). Emit the
separator as a string expression `{' : '}`, which Svelte preserves, restoring
"123 : 123".

ui/src/screens/Lobby.svelte

@@ -267,7 +267,7 @@
                         {#if badge}<span class="unread-dot" class:nudge={badge === 'nudge'}></span>{/if}
                       </span>
                       <span class="sub scoreline"
-                        >{#each orderedSeats(g) as s, i (s.seat)}{#if i > 0}<span class="sep"> : </span
+                        >{#each orderedSeats(g) as s, i (s.seat)}{#if i > 0}<span class="sep">{' : '}</span
                           >{/if}<span
                             class="num"
                             class:win={s.accountId === myId && scoreStanding(g, myId) === 'win'}