#34 [highway-api] Fix JSON placeholder in create modal + Replace event tables with JSON display

Two UI improvements needed: 1. **Create Workflow Modal (#/create)**: When switching to JSON format, the placeholder shows Python DSL example instead of JSON. Should show proper JSON workflow definition example like: ```json { "name": "my_workflow", "start_task": "step1", "tasks": { "step1": { "function": "tools.shell.run", "args": ["echo Hello"] } } } ``` 2. **Events Tab (#/workflow/{id}/events)**: Currently creates HTML tables from event result data. Issues: - Tables make UI slow with large data - Not very useful for viewing complex nested JSON - Should replace with syntax-highlighted prettified JSON display using Prism - Better UX and performance