Swap hand-drawn weather icons for Environment Canada's real icon set

The hand-drawn glyphs (draw_cloud/draw_sun/draw_raindrop/draw_snowflake/
draw_lightning_bolt) are replaced by 7 vendored bitmaps, one per shared
weather category, sourced from weather.gc.ca's public icon set -- these
are small, flat-shaded images that dither cleanly onto the panel's
6-color palette and read as recognizable weather icons in a way the
hand-drawn attempt (a plain circle-with-ticks "sun") didn't. Used for
every provider's rendering (Open-Meteo, NWS, EC), not just when EC is
selected.

Vendored (not fetched live at render time), matching this project's
existing convention for the Noto Emoji fonts -- server/app/weather_icons/
SOURCE.md documents the source, attribution, and the licensing caveat
(this is a personal, non-commercial project; the icon images' own
copyright terms are less clearly permissive than the weather data's own
End-use Licence, since they're served from the public website rather
than ECCC's data servers).

draw_weather_icon's signature changes from (draw, cx, cy, r, category,
palette_rgb) to (img, cx, cy, r, category): pasting a bitmap needs the
Image object, not just an ImageDraw handle, and palette_rgb is no longer
needed since the shared _quantize step already maps whatever's on the
composited canvas to the frame's actual palette -- no per-icon color
resolution required anymore.

server/app/weather/nws.py

@@ -35,8 +35,8 @@ HEADERS = {"User-Agent": "espresso_frame-weather-widget (self-hosted photo frame
 # the same handful of categories Open-Meteo's _CODE_CATEGORIES maps WMO
 # codes to. "wind_"-prefixed variants (e.g. wind_skc) are just the same
 # sky condition plus wind -- stripped before lookup, since this project's
-# hand-drawn icons (app/weather_render.py) don't have a separate windy
-# glyph.
+# vendored icon set (app/weather_render.py, app/weather_icons/) doesn't
+# have a separate windy glyph.
 _ICON_CODE_CATEGORIES = {
     "skc": "clear", "clear": "clear",
     "few": "partly_cloudy", "sct": "partly_cloudy",