This fixes the cache warmup feature by:
- Using WebDriverProxy to perform warmups instead of simple URL fetching
- Caching dashboards instead of individual slices
- Using security_manager.find_user to find user credentials
- Refining WebDriverProxy for multiple operations with persistent driver instance
Originally by @ensky from PR #20387🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: ensky <ensky@users.noreply.github.com>