Cloud agents start 3x faster with builds

Introduced 'builds' for cloud agents, which are pre-prepared copies of development environments. These builds are prepared continuously in the background (defaulting to hourly) and allow agents to boot into a ready environment, reducing setup time and improving response speed by up to 3x. This system ensures that if a new build fails (e.g., due to dependency updates or broken install scripts), agents continue to use the last successful build, maintaining operational continuity. The feature includes enhanced observability in the Cloud Agents dashboard, showing build details, logs, commit SHAs, and associating agent runs with specific builds. The start command still runs when an agent is first prompted, for services that require freshness.