Weather: default to 5-day forecast, add weekday+date header line

- forecast_days now defaults to 5 (was 3) across default_settings(),
  check()'s fallback, and the settings form's pre-selected option.
- New show_date setting (on by default): weekday + date in the same
  "Samstag, 25. Juli" format Clock already used. Combined with the
  city name into one header line above the icon/temp block when both
  are on ("Münster · Samstag, 25. Juli"), each independently
  toggleable.
- Moved the weekday/month name lists and the "Weekday, D. Month"
  formatting out of clock.py into render_utils.format_date_de(), so
  Weather reuses the exact same formatting instead of a second copy
  that could drift.

screens/clock.py

@@ -5,16 +5,10 @@ import time
 from PIL import Image, ImageDraw
 
 from screens.base import Screen
-from screens.render_utils import load_font, text_width
+from screens.render_utils import format_date_de, load_font, text_width
 
 LINE_GAP = 0.04  # fraction of min(width, height) between the time and date lines
 
-WEEKDAYS_DE = ["Montag", "Dienstag", "Mittwoch", "Donnerstag", "Freitag", "Samstag", "Sonntag"]
-MONTHS_DE = [
-    "Januar", "Februar", "März", "April", "Mai", "Juni",
-    "Juli", "August", "September", "Oktober", "November", "Dezember",
-]
-
 
 class ClockScreen(Screen):
     id = "clock"
@@ -31,7 +25,7 @@ class ClockScreen(Screen):
 
         now = time.localtime()
         time_str = state or time.strftime("%H:%M", now)
-        date_str = f"{WEEKDAYS_DE[now.tm_wday]}, {now.tm_mday}. {MONTHS_DE[now.tm_mon - 1]}"
+        date_str = format_date_de(now)
 
         scale = min(width, height)
         time_font = load_font(size=int(scale * 0.32), bold=True)