UI/UX pass: readability, feedback, safer actions, DRK branding

Items 1–12 of the interface review:

- Larger UI font (UI_FONT_SIZE) across widgets, menus, dialogs, Treeview rows.
- DRK-red header bar; window title shows entry count; runtime-drawn red-cross
  icon (also written to data/icon.png for the launcher).
- Status bar colour-coded by severity; transient messages auto-clear after 8 s,
  queue-count messages stay.
- Tab 1: more form spacing, digits-only PLZ, explicit "Auswahl entfernen" +
  Delete key for queue rows, confirm on "Warteschlange leeren", modal on
  duplicate save.
- Tab 2: raw lat/lon columns replaced by one "Karte" column (checkmark / red
  "fehlt"); ▲/▼ arrow on the active sort column; hint line always shows the
  saved-entry count.
- "Karte öffnen" with no coordinates shows a dialog, not just a status line.
- Window size/position remembered between sessions (data/window.json).

Verified by building and driving the window under Homebrew Python 3.12 / Tk 9;
non-GUI smoke tests still pass. Docs updated (changelog, overview, improvements,
data-model, setup, dev-notes).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/README.md

@@ -28,7 +28,7 @@ code) and plots them on an interactive map.
 - **Storage:** one CSV file, `data/orte.csv`
 - **Map:** generated on demand as `data/karte.html` with [Folium](https://python-visualization.github.io/folium/) (Leaflet), opened in the default browser
 - **Geocoding:** OpenStreetMap Nominatim via [`geopy`](https://geopy.readthedocs.io/), rate-limited to 1 request/second on a background thread
-- **UI language:** German
+- **UI language:** German; DRK-red header, enlarged font, colour-coded status bar, window position remembered
 - **Persistence:** atomic CSV writes + rotating backups in `data/backups/`; log at `data/app.log`
 - **Tests:** non-GUI smoke checks only (not yet a committed `tests/` suite)
 - **Version control:** git initialized 2026-09-07