fix: resolve ESLint errors and warnings

- Add emoji accessibility labels (jsx-a11y/accessible-emoji)
- Remove unused imports and variables
- Fix async functions without await
- Add dev directory to ESLint ignore list
- Add eslint-disable comment for necessary console.error
- Clean up unused route file

All ESLint errors resolved (0 errors, 33 warnings remaining)

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

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

dev/app/api/demo/create-payment/route.ts

@@ -44,6 +44,7 @@ export async function POST(request: Request) {
       },
     })
   } catch (error) {
+    // eslint-disable-next-line no-console
     console.error('Failed to create payment:', error)
     return Response.json(
       {