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/calendar_render.py

@@ -414,8 +414,7 @@ def _draw_agenda_day(img: Image.Image, draw: ImageDraw.ImageDraw, day: date, eve
     weather_entries = _weather_for_day(weather_cities, day)
     if weather_entries:
         y += draw_weather_row(img, draw, text_x0, y, text_w, weather_entries,
-                              icon_r=title_font.size // 2, font=weather_font or body_font, units=weather_units,
-                              palette_rgb=palette_rgb)
+                              icon_r=title_font.size // 2, font=weather_font or body_font, units=weather_units)
 
     day_events = _events_on_day(events, day, tz)
     row_h = body_font.size + 14
@@ -637,8 +636,7 @@ def _build_week(events: list[dict], browse_offset: int, target_w: int, target_h:
         weather_entries = _weather_for_day(weather_cities, day)
         if weather_entries:
             y += draw_weather_row(img, draw, x0 + 4, y, col_w - 8, weather_entries,
-                                  icon_r=8, font=weather_font, units=weather_units, show_labels=False,
-                                  palette_rgb=palette_rgb)
+                                  icon_r=8, font=weather_font, units=weather_units, show_labels=False)
         row_h = chip_font.size + 10
         max_rows = max(0, (target_h - MARGIN - y) // row_h)
         day_events = _events_on_day(events, day, tz)