feat: Option to start system automatically

[jkoffman]

Summary

An option to allow the system to start a chosen controller (Buttons Relay, Satellite, Full Companion) and dashboard (on or off) on boot, automatically.

Motivation

• Quicker startup for setups that don't change
• Less chance of someone making the wrong choice at DPX boot

[jkoffman]

In 0.8.0 there doesn't seem to be a way to get back to splash, I think that's what the last commit (after the build 0.8.0) is meant to deal with.

In 0.8.0 restarting does go right back into Companion, so that is working. It doesn't remember the status of the dashboard, so that still has to be fired manually from the web UI.

Maybe a couple of tick boxes in the web UI for autostarting whatever the last mode selected and autostarting the dashboard?

[dubpixel]

Found and fixed the Dashboard-persistence half (commit 043e59c, on fix/action-plan-batch): dpx-dashboard.service's [Install] was WantedBy=graphical.target, but this system deliberately boots to multi-user.target (forced in install-dashboard.sh to work around an unrelated boot-hang bug). Confirmed live on hardware: systemctl is-enabled dpx-dashboard said "enabled" but the symlink lived under graphical.target.wants/, which never activates -- so toggling it on via the web UI worked in the moment (enable --now starts it immediately) but never survived a reboot. Changed to WantedBy=multi-user.target.

With that fix, no extra checkbox should be needed for either half of your ask -- "last mode" already autostarts via dpx-mode-select.service (from #11/#12's original fix, which you already confirmed working in 0.8.0), and Dashboard's own enabled/disabled state will now actually persist the same way. Will need a real reboot test on hardware with a display to fully confirm the Dashboard half -- leaving open until then.