Declutter the challenge panel and obstacle titles (v4)

Per playtest feedback:
- Drop the per-challenge 'Plays:' line — redundant with the card column and the
  event log (also removes the now-unused chPlays const).
- Drop the 'Attempted by … drag a card … assist' how-to paragraph; players know
  the basics, and the challenge header already names who's challenged.
- Replace the 'Red/Black Obstacle · match to draw' tag with the original card in
  the title (e.g. '5♣ — Loitering Mermaid'), and color the title by suit. The
  left border already marks color; the dead .obstacle-color-tag CSS is removed.

Suit glyphs in the title use plain text symbols (not SUIT_EMOJI) so they take
the theme-aware suit color and stay readable on the dark panel. Verified in
light and dark.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/scene/ChallengePanel.svelte

@@ -95,7 +95,6 @@
 {/if}
 
 {#each openChallenges as ch}
-    {@const chPlays = JSON.parse(ch.plays || '[]')}
     {@const chObstacleIds = JSON.parse(ch.obstacle_ids || '[]')}
     <div class="challenge-item">
         <div class="challenge-head">
@@ -127,10 +126,6 @@
                 Temporary Obstacle: <strong use:tooltip={{ html: cardTooltipHtml(ch.temp_card, $obstacleTable) }}>{getCardDisplay(ch.temp_card)}</strong> — {playerName(ch.acting_player_id)} must answer it!
             </p>
         {:else}
-            <p class="info-text" style="margin: 0.5rem 0 0 0;">
-                Attempted by <strong>{playerName(ch.acting_player_id)}</strong>{ch.acting_player_id !== ch.target_player_id ? ` (took it over via ${ch.tax_type === 'gat' ? 'Gat' : 'Name'} Tax)` : ''}.
-                Drag a card onto an Obstacle below to play it. Other Pi-Rats may assist (assistants don't draw back).
-            </p>
             <div class="challenge-obstacles">
                 {#each chObstacleIds as oid}
                     {@const obs = state.obstacles.find(o => o.id === oid)}
@@ -142,12 +137,6 @@
                 {/each}
             </div>
         {/if}
-        {#if chPlays.length > 0}
-            <p class="info-text" style="margin: 0.5rem 0 0 0; font-size: 0.85rem;">
-                Plays: {chPlays.map(p => `${p.player_name}: ${getCardDisplay(p.card)} ${p.success ? '✔' : '✘'}`).join(' · ')}
-            </p>
-        {/if}
-
         <!-- Tax: pending request aimed at me -->
         {#if ch.tax_state === 'requested'}
             {#if myTaxRequest && myTaxRequest.id === ch.id}