Merge origin/main: reconcile briefing checklist and brief visuals

Both branches added a case-briefing checklist independently. Reconcile onto
the upstream {id,text} BriefChecklistItem model and keep the upstream brief /
luggage-tag visual refinements (boxed CHECKLIST section, assignment/heading
split), while retaining this branch's full-stack backing (checklist table,
board read/write/clone, importer/exporter) and the player-tickable interaction
(persisted locally per level). Keep the brief-goals list alongside the new
checklist. Align the server wire shape, importer, and exporter to {id,text}.

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

scripts/importMysteryTemplate.ts

@@ -116,7 +116,7 @@ async function importLevel(baseUrl: string, folderDir: string, level: MysteryLev
   }
 
   const folderIds = new Map(levelFolders.map(folder => [folder.key, randomUUID()]))
-  if (level.brief) state.brief = { body: level.brief.body, concepts: (level.brief.concepts || []).map(concept => ({ id: randomUUID(), ...concept })), checklist: level.brief.checklist }
+  if (level.brief) state.brief = { body: level.brief.body, concepts: (level.brief.concepts || []).map(concept => ({ id: randomUUID(), ...concept })), checklist: (level.brief.checklist || []).map(text => ({ id: randomUUID(), text })) }
   state.views = state.views.map(view => view.type === 'timeline' ? { ...view, rangeMode: level.timelineRange ? 'fixed' : 'auto', range: level.timelineRange } : view)
   const folders = levelFolders.map(folder => ({
     id: folderIds.get(folder.key)!, type: 'folder', title: folder.title, content: folder.content,