Polish: legible crew roster, End-Scene enforcement, decluttered Hand

- Crew roster bubbles: explicit text color + opaque distinct surface so
  they're legible and stand out from the page in both themes (the bug was
  the <button> defaulting to black-on-dark in dark mode).
- End-Scene enforcement: unless Dev Mode is on, a scene can't end until
  every living Pi-Rat has faced a Deep Challenge or the Obstacle List is
  empty. end_scene_and_transition now returns (ok, msg) and the route
  surfaces a 400; the Deep sees a ✓/○ challenge-progress badge on each
  Pi-Rat bubble. 3 new tests cover the gate.
- Hand panel: dropped the how-to-play blurb and the title in favor of a
  low-profile "Your Hand" label.
- Bump VERSION to 8 with changelog entry; check off TODO.md Polish items.

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

frontend/src/components/scene/CrewColumn.svelte

@@ -2,6 +2,7 @@
     import { slide } from 'svelte/transition';
     import { apiRequest } from '../../lib/api';
     import { crewLabel } from '../../lib/cards';
+    import { tooltip } from '../../lib/tooltip';
     import CharacterSheet from './CharacterSheet.svelte';
 
     export let state;
@@ -12,6 +13,17 @@
 
     $: isDeep = state.player.role === 'deep';
 
+    // Track which Pi-Rats have faced a Deep Challenge this scene so the Deep can
+    // see who still needs one before ending the scene.
+    $: challengedIds = new Set(
+        (state.challenges || [])
+            .filter(c => c.challenge_type === 'deep')
+            .map(c => c.target_player_id)
+    );
+    function hasBeenChallenged(p) {
+        return p.role === 'pirat' && challengedIds.has(p.id);
+    }
+
     // The Deep ticks Crew Objectives off here (moved from the old Deep panel).
     async function toggleCrew(type) {
         objError = '';
@@ -51,6 +63,15 @@
                 title="View {p.name}'s character sheet"
                 on:click={() => openTargetId = p.id}
             >
+                {#if isDeep && p.role === 'pirat'}
+                    <span
+                        class="challenge-check"
+                        class:done={hasBeenChallenged(p)}
+                        use:tooltip={hasBeenChallenged(p)
+                            ? `${p.name} has faced a Challenge this scene.`
+                            : `${p.name} hasn't faced a Challenge yet — the scene can't end until they do (or the Obstacle List is cleared).`}
+                    >{hasBeenChallenged(p) ? '✓' : '○'}</span>
+                {/if}
                 <span class="bubble-icon">{roleIcon(p)}</span>
                 <span class="bubble-name">{crewLabel(p, captainId)}</span>
                 <span class="bubble-meta">