Add install.sh / run.sh / bundled icon; fully pin requirements

- install.sh: one-time Linux Mint setup (apt, .venv, requirements, .desktop
  entry with absolute paths). Re-runnable.
- run.sh: launches the app from .venv (called by the menu entry).
- icon.png: bundled 256px red-cross launcher/window icon; app prefers it over
  the runtime-drawn fallback (data/icon.png).
- requirements.txt: fully pinned incl. transitive deps, tested on Python 3.12;
  numpy held at 2.2.6 so it installs on Python 3.10 too.

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

app.py

@@ -40,7 +40,8 @@ CSV_PATH = DATA_DIR / "orte.csv"
 MAP_PATH = DATA_DIR / "karte.html"
 BACKUP_DIR = DATA_DIR / "backups"
 LOG_PATH = DATA_DIR / "app.log"
-ICON_PATH = DATA_DIR / "icon.png"
+ICON_PATH = BASE_DIR / "icon.png"          # mitgeliefert (für Fenster + Startmenü)
+ICON_FALLBACK_PATH = DATA_DIR / "icon.png"  # zur Laufzeit gezeichnet, falls obiges fehlt
 WINDOW_STATE_PATH = DATA_DIR / "window.json"
 CSV_COLUMNS = ["date", "city", "postal_code", "lat", "lon"]
 
@@ -735,8 +736,12 @@ class App(ttk.Window):
         )
 
     def _install_icon(self) -> None:
-        """Zeichnet ein einfaches rotes Kreuz als Fenster-Icon (ohne Extra-Abhängigkeit)."""
+        """Setzt das Fenster-Icon: mitgelieferte icon.png, sonst ein gezeichnetes Kreuz."""
         try:
+            if ICON_PATH.exists():
+                self._icon_img = tk.PhotoImage(file=str(ICON_PATH))
+                self.iconphoto(True, self._icon_img)
+                return
             size = 64
             img = tk.PhotoImage(width=size, height=size)
             img.put("white", to=(0, 0, size, size))
@@ -745,11 +750,10 @@ class App(ttk.Window):
             img.put(DRK_RED, to=(7, arm, size - 7, size - arm))
             self.iconphoto(True, img)
             self._icon_img = img  # Referenz halten
-            if not ICON_PATH.exists():
-                try:
-                    img.write(str(ICON_PATH), format="png")
-                except tk.TclError:
-                    pass  # Tk < 8.6 kann kein PNG schreiben – nicht kritisch
+            try:
+                img.write(str(ICON_FALLBACK_PATH), format="png")
+            except tk.TclError:
+                pass  # Tk < 8.6 kann kein PNG schreiben – nicht kritisch
         except tk.TclError:
             log.warning("Fenster-Icon konnte nicht gesetzt werden.")