Introduces app/panel_style.py, a shared style module every render
module now draws through instead of independently duplicating margins/
colors/fonts: Inter Bold/Regular (already vendored, previously only
used by widgets/text.py) replace PIL's single-weight bundled default
font everywhere else; a per-widget-kind accent color (calendar=blue,
tasks=green, weather=black header) replaces plain black-on-white chrome
and is centralized in one THEME mapping so a future global theme only
needs to touch panel_style.py; a small per-widget gutter separates
adjacent widgets without touching grid.py's cell math; header bars,
color chips, and the battery icon get rounded corners.
Also drops the MUTED gray text color used throughout calendar_render.py
and weather_render.py -- a non-palette color that has no close match in
the panel's 6-ink palette and dithers into visible speckle once the
composited canvas is quantized. Secondary text now reads through size/
weight alone, always exact black.
widgets/battery.py and manage_overlay.py's previously-duplicated
battery-glyph-drawing code now share one implementation (panel_style.
draw_battery_icon). widgets/_shared.py's placeholder image is fixed to
use exact palette colors and route through image_pipeline.draw_text,
same as everything else -- it was quietly violating both rules already.
image_pipeline.draw_widget_border gains an opt-in radius param (default
0, unused by any call site) for a possible future rounded-border
setting -- doesn't touch the exact-corner-pixel behavior test_widget_
border.py already pins.
Deliberately out of scope: DEFAULT_PALETTE_RGB and the Floyd-Steinberg
quantization pipeline are untouched, per the prior reverted measured-
palette/OKLab attempt (05b417a/dfe9d701).
