Initial commit: Arbeitsorte-Logger + data-safety/robustness/input work

Existing app (single-file Tkinter/ttkbootstrap desktop tool for logging
blood-drive work assignments and mapping them) plus the first round of
improvements:

- Data safety: atomic CSV writes (tmp + fsync + os.replace), rotating
  backups in data/backups/ (startup + before every change, keep 20),
  fallback to empty/backup on missing/empty/corrupt orte.csv.
- Geocoder robustness: per-item try/except so the worker thread survives
  failures; GeocodingUnavailable + one-time "service unreachable" dialog.
- Input: DateEntry calendar picker with parse_date() validation; manual
  lat/lon fields in the edit dialog; Tab 2 highlights/filters rows without
  coordinates and adds a right-click "Koordinaten suchen".
- Logging to data/app.log; shared autocomplete helpers; config constants;
  map fit_bounds.

docs/ describes current state, architecture, data model, setup (Linux Mint),
and the full improvement roadmap. data/orte.csv is gitignored for now.

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

docs/setup.md

@@ -0,0 +1,105 @@
+# Setup & running
+
+Target machine: **Linux Mint laptop**, single non-technical user. The goal is
+that day-to-day use is a **double-click**, with the terminal only needed once
+during install.
+
+## 1. System packages
+
+Tkinter is not bundled with the system Python on Mint and must be installed
+separately:
+
+```bash
+sudo apt update
+sudo apt install python3-tk python3-venv python3-pip
+```
+
+## 2. Get the code
+
+Put the project folder somewhere stable, e.g. `~/Apps/DRK_Blutspende_Orte`.
+
+## 3. Create a virtual environment and install dependencies
+
+```bash
+cd ~/Apps/DRK_Blutspende_Orte
+python3 -m venv .venv
+.venv/bin/pip install -r requirements.txt
+```
+
+`requirements.txt`:
+
+```
+ttkbootstrap==1.10.1
+geopy>=2.4.1
+folium>=0.17.0
+pandas>=2.2.0
+```
+
+> Only `ttkbootstrap` is pinned exactly. For a machine you hand to someone else,
+> consider pinning all four (see [improvements.md](improvements.md#5-packaging--distribution)).
+
+## 4. Run it
+
+```bash
+.venv/bin/python app.py
+```
+
+The window should open. `data/orte.csv` is created automatically on first run if
+it is missing.
+
+## 5. Make it a double-click launcher
+
+### Launcher script
+
+Create `run.sh` in the project root:
+
+```bash
+#!/usr/bin/env bash
+cd "$(dirname "$0")"
+exec .venv/bin/python app.py
+```
+
+```bash
+chmod +x run.sh
+```
+
+### Desktop entry
+
+Create `~/.local/share/applications/drk-blutspende-orte.desktop`:
+
+```ini
+[Desktop Entry]
+Type=Application
+Name=DRK Blutspende – Arbeitsorte
+Comment=Einsatzorte protokollieren und auf der Karte anzeigen
+Exec=/home/USER/Apps/DRK_Blutspende_Orte/run.sh
+Icon=/home/USER/Apps/DRK_Blutspende_Orte/icon.png
+Terminal=false
+Categories=Utility;
+```
+
+Replace `USER` with the real username. Add any PNG as `icon.png` (the DRK logo
+works well). The entry then shows up in the Mint menu and can be pinned to the
+panel or the desktop.
+
+## Python / Tk version
+
+Python 3.9+ is fine (the code uses `from __future__ import annotations`). The
+system Python on current Mint releases is well above that.
+
+`ttkbootstrap` needs **Tk 8.6 or newer**. Linux Mint's `python3-tk` provides
+that. The macOS CommandLineTools Python used during development ships Tk 8.5 and
+**cannot run the GUI** — see [dev-notes.md](dev-notes.md).
+
+## Updating
+
+```bash
+cd ~/Apps/DRK_Blutspende_Orte
+git pull            # once the project is in git
+.venv/bin/pip install -r requirements.txt
+```
+
+## Data location
+
+All state is in `data/orte.csv` next to `app.py`. To back up the app, copy that
+one file. To move to a new laptop, copy the whole folder and redo steps 1 & 3.