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/overview.md

@@ -1,6 +1,11 @@
 # Overview – what the app does
 
-The app is a single window with a status bar at the bottom and two tabs.
+The app is a single window: a **DRK-red header bar**, two tabs, and a
+**colour-coded status bar** at the bottom (grey = neutral, green = success,
+orange = warning, red = error; transient messages fade back to neutral after
+~8 s). The window title shows the total entry count, and the window remembers
+its size and position between sessions (`data/window.json`). The UI font is
+enlarged for readability (`UI_FONT_SIZE`).
 
 ## Tab 1 – "Neuer Eintrag" (new entry)
 
@@ -12,28 +17,34 @@ then save the whole batch at once.
    `TT.MM.JJJJ` and **validated** – an invalid date is rejected with a dialog),
    city (autocomplete combobox), postal code (optional). Pressing `Return` in any
    field, or the **+ Hinzufügen** button, adds the row to the queue.
+   The PLZ field only accepts digits.
 2. **Queue table** – shows date, city, PLZ, and a live coordinate column that
    updates from `⏳ wird gesucht…` to either `lat / lon` or `⚠ nicht gefunden`
    as the background geocoder works through the queue.
-   - Left-click the `✕` cell to remove a row.
+   - Select a row and press <kbd>Delete</kbd>, use the **"Auswahl entfernen"**
+     button, or click the `✕` cell.
    - Right-click a row for *Löschen* / *Koordinaten erneut suchen*.
 3. **Action bar**
-   - **Alle speichern** – appends every queued row to `orte.csv`. If a row looks
-     like a duplicate of an existing entry (same date + city + PLZ) a hint is
-     shown in the status bar, but the row is **still saved**.
-   - **Leeren** – discards the queue without saving.
+   - **Alle speichern** – appends every queued row to `orte.csv`. If any row
+     looks like a duplicate (same date + city + PLZ), a **modal** lists them and
+     asks whether to save anyway.
+   - **Warteschlange leeren** – discards the queue (asks for confirmation).
    - **Karte öffnen** – regenerates `karte.html` and opens it in the browser.
 
 ## Tab 2 – "Einträge verwalten" (manage entries)
 
 A table view of everything in `orte.csv`.
 
+- **Columns:** Datum, Ort, PLZ, and **Karte** – a status column showing `✓` when
+  the row has coordinates or a red `fehlt` when it doesn't (the whole row is red
+  too). The raw lat/lon numbers live in the edit dialog, not this table.
 - **Search box** – live filter across date, city, and PLZ (substring match).
-- **Sortable columns** – click a header to sort; clicking again reverses.
-  Default sort is by date, newest first.
+- **Sortable columns** – click a header to sort; clicking again reverses. The
+  active column shows a ▲/▼ arrow. Default sort is by date, newest first.
+  Sorting by **Karte** groups the rows without coordinates together.
 - **"Nur ohne Koordinaten"** toggle – filters to entries that have no
-  coordinates yet. Such rows are also shown in **red** in the full list, and the
-  hint line reports how many there are.
+  coordinates yet. The hint line always shows the total count, plus how many are
+  missing coordinates.
 - **Edit** – double-click a row (or *Bearbeiten*) opens a modal dialog to change
   date (calendar picker, validated) / city / PLZ. Two ways to fix coordinates:
   a "Koordinaten automatisch neu suchen" toggle re-runs geocoding after saving,
@@ -58,8 +69,8 @@ Generated by `generate_map()`:
   (`5 + count / max_count * 20` px), colour is DRK red (`#CC0000`).
 - Popup shows the city and the visit count; tooltip shows the city.
 - Rows with missing/blank coordinates are silently excluded.
-- If there are no usable coordinates at all, a `ValueError` is raised and shown
-  in the status bar.
+- If there are no usable coordinates at all, a dialog says so (and the status
+  bar shows a warning).
 
 > The generated HTML pulls Leaflet, jQuery and Bootstrap from CDNs, so the map
 > needs an internet connection to render even though the data is local.