fix(kanban): resolve hardcoded model display in cards

- Fix model string validation in feature executor
- Remove hardcoded opus 4.5 references
- Update kanban card to show actual selected model
- Clean up completed feature contexts
- Standardize feature list with model/thinking fields

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

app/src/components/views/kanban-card.tsx

@@ -326,7 +326,7 @@ export function KanbanCard({
               <div className="flex items-center gap-1 text-cyan-400">
                 <Cpu className="w-3 h-3" />
                 <span className="font-medium">
-                  {formatModelName(DEFAULT_MODEL)}
+                  {formatModelName(feature.model ?? DEFAULT_MODEL)}
                 </span>
               </div>
               {agentInfo.currentPhase && (