* constellation: crash to a new “sad tab” page
* check in resources/crash.html
* use a separate enum variant instead of keying on reason
* fmt + tidy
* rename Resource::Crash to Resource::CrashHTML
* clean up crash page and add details (reason + backtrace)
* avoid repeating crash errors in script::script_thread warn log
* make new LoadData init more idiomatic
* clarify comments and new fields
* fix doc comment style
