Add configurable letterbox fill for sleep screen cover images that don't
match the display aspect ratio. Four fill modes are available: Solid
(single dominant edge shade), Blended (per-pixel edge colors), Gradient
(edge colors interpolated toward white/black), and None.
Enable upscaling of cover images smaller than the display in Fit mode by
modifying drawBitmap/drawBitmap1Bit to support both up and downscaling
via a unified block-fill approach.
Edge sampling data is cached to .crosspoint alongside the cover BMP to
avoid redundant bitmap scanning on subsequent sleeps. Cache is validated
against screen dimensions and auto-regenerated when stale.
New settings: Letterbox Fill (None/Solid/Blended/Gradient) and Gradient
Direction (To White/To Black).
Co-authored-by: Cursor <cursoragent@cursor.com>
4edb14bdd9
