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/dev-notes.md

@@ -3,23 +3,31 @@
 Running list so the same mistakes aren't repeated. Add to it whenever reality
 contradicts an assumption.
 
-## The GUI does not run on the development Mac (2026-09-07)
+## The macOS system Python can't run the GUI; use a Homebrew Python (2026-09-07)
 
 The macOS **CommandLineTools** Python 3.9 (`/Library/Developer/CommandLineTools/
 .../python3.9`) ships **Tk 8.5.9**. `ttkbootstrap` 1.10.1 requires **Tk 8.6+**.
+Symptoms: `TclError: couldn't recognize image data` (window icon) and
+`TclError: unknown option "-style"` on `ttk.Scrollbar`.
 
-Symptoms when trying to launch `App()` there:
-- `_tkinter.TclError: couldn't recognize image data` (ttkbootstrap's window icon
-  is a PNG; Tk 8.5 can't decode it), and
-- `_tkinter.TclError: unknown option "-style"` on `ttk.Scrollbar`.
+**Fix for local GUI testing:** `brew install python-tk@3.12` (pulls `tcl-tk`,
+gives Python 3.12 + **Tk 9.0**), then:
 
-Consequences:
-- `app.py` **cannot be smoke-tested through the GUI on this machine.** Logic is
-  covered by a non-GUI script (constructs `DataStore`, exercises helpers and the
-  worker with monkey-patched paths).
-- The **Linux Mint target is unaffected** — its system Tk is 8.6.
-- If GUI testing on macOS is ever needed, install a Homebrew
-  `python-tk@3.x` / `tcl-tk` combo, or use `pyenv` with `--with-tcltk`.
+```bash
+/opt/homebrew/bin/python3.12 -m venv venv
+venv/bin/pip install -r requirements.txt
+venv/bin/python app.py
+```
+
+`ttkbootstrap` 1.10.1 runs fine on Tk 9.0 in practice (verified: window builds,
+Treeview sort, DateEntry, LabelFrame, custom styles all work).
+
+- The **Linux Mint target** uses its own `python3-tk` (Tk 8.6+) and is
+  unaffected either way.
+- `screencapture` from a non-GUI shell fails ("could not create image from
+  display") without Screen-Recording permission — automated screenshots of the
+  running app aren't available here; verify by building the widget tree and
+  driving it programmatically instead.
 
 ## `pandas` reads everything as strings by design