Add isolated macro storage and dedicated macro management

[Q1WP]

Test deployment: http://bbctrl.dyndns.org:8091/

Fixes #346.
Fixes #347.

This PR contains the macro-related changes requested after the earlier mixed
PRs.

Changes:

• Macro isolation: macro source files are copied into protected Home/macros
  storage on save/load migration. Older configs are migrated automatically, and
  orphaned protected macro files are cleaned up.
• Reference system: macros can require referenced axes before run. Homed axes
  are referenced automatically, and manually set positions also establish
  reference.
• skip_reference_check: per-macro override for homing/setup macros that must
  run before axes are referenced.
• Restore behavior: after a macro finishes, the previous active program is
  restored.
• Macros page: moves macro management out of Settings -> Macros into a
  dedicated top-level page.
• Tabs/visibility/confirm: macros can be organized into tabs, hidden from the
  control page, and optionally confirmed before run.
• ZEROED state: referenced-but-not-homed axes are shown separately from fully
  unreferenced axes.
• Protected file access: protected macro directories are hidden from the normal
  file browser, but active macro files remain readable so the control page,
  editor, and toolpath viewer still work.
• Control-page preflight: missing-reference errors are caught before the run
  confirm dialog, which avoids confirm-then-fail behavior.

Implementation notes:

• macro isolation copies source files into protected storage; source files are
  not renamed or modified
• protected macro paths cannot be written or deleted through the normal file
  APIs
• direct reads of active protected macro files remain allowed so the control
  page, editor, and toolpath viewer work while a macro is running

Validation:

• python3 -m py_compile on changed Python files
• node -c on changed JS files
• controller testing covered macro creation/edit/save, migration, tabs,
  visibility, confirm on/off, skip_reference_check, active macro display, and
  logged-out/read-only macro editing

[jcoffland]

Sorry, it's taking me awhile to get time to look at these in detail. I've seen they exist and will look at them as soon as I get a chance. I'm traveling a lot right now.