Last step of splitting static/style.css by panel. This moves the cookbook,
deep research, memory and settings rules that can move into
static/css/cookbook-research-memory-settings.css.
After the three steps style.css still holds the shell and every rule whose
move would change the cascade, which on this branch is most of the file.
Eager ordered links, verbatim moves, no rendering change.
Second step of splitting static/style.css by panel. This moves the email,
calendar, notes and tasks rules that can move into
static/css/email-calendar-notes-tasks.css.
Same shape as the first step: eager ordered links, verbatim moves, no
rendering change. The header comment in each split file lists the load order
and the earlier file's header is updated so all of them agree.
Alexandre Teixeira