All screens: drop gray text, matching the Journey fix

The epd4in0e panel's palette has no gray at all (just black/white/
yellow/red/blue/green -- see epd4in0e.py's putpalette), so any gray
RGB fill gets Floyd-Steinberg dithered into a black/white checkerboard
across the whole glyph body. At the small font sizes most of these
screens use (Navidrome's artist/album/genre/source lines, Departures'
direction/platform columns, Weather's description/forecast labels,
Clock's date line, the placeholder messages), that reads as blurry,
half-rendered text -- same root cause already fixed in Journey.

Switched every gray fill/outline to solid black across navidrome.py,
weather.py, departures.py, clock.py, and picture.py. Left the
intentionally-faint row-divider hairlines (228,228,228) alone --
those are meant to almost disappear, not readable text. Removed
departures.py's now-unused MUTED constant.

screens/departures.py

@@ -30,7 +30,6 @@ RESULTS_CHOICES = (3, 5, 8)
 
 BLACK = (0, 0, 0)
 RED = (200, 0, 0)
-MUTED = (110, 110, 110)
 FAINT_LINE = (228, 228, 228)
 
 
@@ -167,7 +166,7 @@ class DeparturesScreen(Screen):
             self._draw_centered_v(draw, line_text, line_font, pad, row_cy, BLACK)
 
             direction = truncate_to_width(draw, dep["direction"], dir_font, dir_w - 10)
-            self._draw_centered_v(draw, direction, dir_font, dir_x, row_cy, (60, 60, 60))
+            self._draw_centered_v(draw, direction, dir_font, dir_x, row_cy, BLACK)
 
             if dep["cancelled"]:
                 time_text, time_color = "Fällt aus", RED
@@ -184,7 +183,7 @@ class DeparturesScreen(Screen):
                 pw = text_width(draw, platform_text, platform_font)
                 self._draw_centered_v(
                     draw, platform_text, platform_font,
-                    platform_x + (platform_w - pw) / 2, row_cy, MUTED,
+                    platform_x + (platform_w - pw) / 2, row_cy, BLACK,
                 )
 
         return image
@@ -192,7 +191,7 @@ class DeparturesScreen(Screen):
     def _render_message(self, draw, width, height, scale, msg):
         font = load_font(size=int(scale * 0.06))
         mw = text_width(draw, msg, font)
-        draw.text(((width - mw) / 2, height / 2), msg, font=font, fill=MUTED)
+        draw.text(((width - mw) / 2, height / 2), msg, font=font, fill=BLACK)
 
     def _draw_centered_v(self, draw, text, font, x, cy, fill):
         left, top, right, bottom = draw.textbbox((0, 0), text, font=font)