FEATURE: h8 set command — toggle container entrypoint

[erfanium]

Problem

No CLI command to change the container entrypoint. Needed for:

• Debug mode: h8 set command myapp "sleep 3600" to keep container alive for exec
• Restore: h8 set command myapp --reset to go back to Docker entrypoint

Workaround

Raw API call:

curl -X PUT .../apps/xxx/ -d '{"command":"sleep 3600"}'

But this requires also including subdomain, SSL, disk, and envs to avoid wiping them (see #8).

Proposal

h8 set command myapp "sleep 3600"     # override entrypoint
h8 set command myapp --reset            # back to Docker default

[erfanium]

Real-world use case from today: migrating a Grist server to a new cluster. I needed to:

1. Set command to "sleep 3600" to stop Grist and keep the container alive
2. Extract a backup tarball onto the persistent disk
3. Restore command to null (back to Docker entrypoint)

This required 3 raw API calls, each with full field preservation to avoid wiping subdomain/SSL/disk. A simple h8 set command grist "sleep 3600" → h8 set command grist --reset would have turned 10 minutes of careful curl/JSON crafting into 10 seconds.