Fuse is good, battery voltage to fuse.Relays traded with known good ones (I have 3 HHR's).
Of course, previous owner never had these problems, no known immobilizer.

 

Problem finally solved!

2009 HHR SS Panel. One of the 18 Canadian Panels!!

After a month of trying to find the source of the problem (and with outside help), the HHR is finally back on the road.
Everything is working as it should (cranks/starts, headlights working, power seat working, and center RPD working.
Finally came down to replacing the entire fuse block due to internal corrosion.

Thanks to all who gave advice. A little bit of many replies saved the day!

 

Fuse block internally corroded. Problem resolved, awesome!

 

Yes; happy day, happy day!

FWIW, the block didn't look too terribly bad. New replacements are NLA-discontinued by Chevrolet!
Pn GM 20908792 fits 09-11 HHR with power seat
I'll look for clean spares in the wrecking yards!