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/render_utils.py

@@ -6,6 +6,7 @@ dithering by default) -- so screens can draw with normal anti-aliased RGB
 text and full-color cover art without worrying about the palette themselves.
 """
 
+import time
 from pathlib import Path
 
 from PIL import Image, ImageFont
@@ -14,6 +15,17 @@ FONTS_DIR = Path(__file__).resolve().parent.parent / "fonts"
 
 _font_cache: dict[tuple[str, int], ImageFont.FreeTypeFont] = {}
 
+WEEKDAYS_DE = ["Montag", "Dienstag", "Mittwoch", "Donnerstag", "Freitag", "Samstag", "Sonntag"]
+MONTHS_DE = [
+    "Januar", "Februar", "März", "April", "Mai", "Juni",
+    "Juli", "August", "September", "Oktober", "November", "Dezember",
+]
+
+
+def format_date_de(t: time.struct_time | None = None) -> str:
+    t = t or time.localtime()
+    return f"{WEEKDAYS_DE[t.tm_wday]}, {t.tm_mday}. {MONTHS_DE[t.tm_mon - 1]}"
+
 
 def load_font(size: int, bold: bool = False) -> ImageFont.FreeTypeFont:
     key = ("bold" if bold else "regular", size)