Revert to hand-drawn weather icons, styled after EC's set but exact panel colors

The vendored EC bitmaps looked good but dither into a visible speckle
once quantized to the panel's 6-color palette (their colors are
anti-aliased/arbitrary RGB, essentially never an exact palette match).
Hand-drawn icons filled with the frame's actual ink colors quantize with
zero dithering error to diffuse -- confirmed by running both through the
real quantize pass: the bitmap version speckles, the hand-drawn one is
pixel-identical before and after.

Redrawn to look more like EC's style this time around: pointed
triangular sun rays (the earlier attempt's thin-line rays read as a
crosshair, not a sun) and dendrite snowflakes (tick marks near each tip,
not a bare asterisk), plus the same cloud/raindrop/lightning-bolt shapes
as before. Removed the vendored server/app/weather_icons/ directory
entirely -- no longer used, and removes the icon-image licensing
question along with it.

server/app/calendar_render.py

@@ -414,7 +414,8 @@ 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)
+                              icon_r=title_font.size // 2, font=weather_font or body_font, units=weather_units,
+                              palette_rgb=palette_rgb)
 
     day_events = _events_on_day(events, day, tz)
     row_h = body_font.size + 14
@@ -636,7 +637,8 @@ 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)
+                                  icon_r=8, font=weather_font, units=weather_units, show_labels=False,
+                                  palette_rgb=palette_rgb)
         row_h = chip_font.size + 10
         max_rows = max(0, (target_h - MARGIN - y) // row_h)
         day_events = _events_on_day(events, day, tz)