feat: add docker runtime TTL; better runtime connection & feedback

[lihebi]

Add two timers for runtime:

• last active time: this is the last time a runtime session is connected. The runtime will be terminated 12h after the last active time. Opening the repo (and connecting the runtime) will refresh the last active record.
• up time: the is when the runtime is started

On the dashboard, show the runtime's last active time for each repo.

On the repo canvas page, the sidebar shows the up time.

[lihebi]

This PR implements the docker runtime TTL. A k8s runtime TTL shall be implemented in another PR.

This PR also maintains a better runtime connection & feedback. The runtime will try re-connect automatically, so there won't be a "connect" button anymore.