Add notebook sleep screens

[MRoiban]

What changed

• add native Show notebook on sleep and Cover / Current page controls
  under Kobo's power settings
• substitute a notebook image only when a visible Advanced Notebook is active
  at the sleep or power-off boundary
• composite current-page ink over the active built-in or custom template using
  the live MyScript renderer transform
• suppress stale book reading status while a notebook image is displayed
• add firmware ABI pins, instruction proofs, regression checks, and a replayable
  bnremote_api investigation

Why

Kobo normally shows the last book cover even when the device is put to sleep
from an Advanced Notebook. Notebook users need the option to retain the active
notebook context without changing book-reader behavior.

The alignment defects found during device testing came from treating MyScript's
right/bottom extent coordinates as width/height and from ignoring the renderer's
live affine transform. The compositor now restores the exported ink to its exact
page-space extent, zoom, pan, and canvas offset.

User impact

When enabled, sleeping or powering off from a visible notebook shows its cover
or current page, including its paper template. Sleeping from a book or any
non-notebook view preserves Kobo's stock cover behavior. Rendering failures
also fail closed to the stock cover.

Validation

• make -C mods/custom-notebook-templates check
• complete firmware ABI verification: 128 symbols, 5 vtable sizes, 31 vtable
  slots, 139 instruction pins, and 9 jump slots
• clean NickelTC GCC 4.9.4 ARM hard-float build with VERSION=v0.0.3-alpha
• compiled layer-preview ABI verification
• exact two-file installer and embedded-version verification
• on-device confirmation on Kobo Elipsa 2E (condor) firmware 4.38.23697,
  including current-page/template alignment and native settings alignment