[PR 11] Workflow UI + Agent Configuration Browser

Implement workflow listing, DAG visualization, and agent configuration viewer.

## What to implement

### Workflow UI

- `/opsml/workflows/` — list of workflows with DAG preview
- `/opsml/workflows/[space]/[name]/` — full DAG visualization, step details, "Run locally" button

### Agent Configuration Browser

- `/opsml/agents/[space]/[name]/` — agent config viewer: model, skills, tools, permissions
- "Configure for CLI" button → server generates config files, returns zip or instructions

## Verification

```bash
make dev.both
# Navigate to workflow list
# View DAG visualization
# View agent config
```

## Depends on

- #359 (PR 10)

## Blocks

- #361 (PR 12)