Add on-canvas navigation arrows

app/gui/ui.py

@@ -16,8 +16,6 @@ class UIBuilderMixin:
         buttons = [
             ("📂 Bild laden", self.load_image),
             ("📁 Ordner laden", self.load_folder),
-            ("⬅️ Bild zurück", self.show_previous_image),
-            ("➡️ Nächstes Bild", self.show_next_image),
             ("🎨 Farbe wählen", self.choose_color),
             ("🖱️Farbe aus Bild klicken", self.enable_pick_mode),
             ("💾 Overlay speichern", self.save_overlay),
@@ -74,6 +72,8 @@ class UIBuilderMixin:
         left_column = ttk.Frame(main)
         left_column.pack(side=tk.LEFT, fill=tk.BOTH, expand=True, padx=(0, 6))
 
+        self._create_navigation_button(left_column, "◀", self.show_previous_image)
+
         self.canvas_orig = tk.Canvas(left_column, bg="#1e1e1e", highlightthickness=0, relief="flat")
         self.canvas_orig.pack(fill=tk.BOTH, expand=True)
         self.canvas_orig.bind("<Button-1>", self.on_canvas_click)
@@ -86,6 +86,7 @@ class UIBuilderMixin:
 
         self.canvas_overlay = tk.Canvas(right_column, bg="#1e1e1e", highlightthickness=0, relief="flat")
         self.canvas_overlay.pack(fill=tk.BOTH, expand=True)
+        self._create_navigation_button(right_column, "▶", self.show_next_image)
 
         info_frame = ttk.Frame(self.root)
         info_frame.pack(fill=tk.X, padx=12, pady=(0, 12))
@@ -316,6 +317,25 @@ class UIBuilderMixin:
         ]
         return canvas.create_polygon(points, smooth=True, splinesteps=24, **kwargs)
 
+    def _create_navigation_button(self, container, symbol: str, command) -> None:
+        wrapper = ttk.Frame(container)
+        wrapper.pack(fill=tk.Y)
+
+        btn = tk.Button(
+            wrapper,
+            text=symbol,
+            command=command,
+            font=("Segoe UI", 18, "bold"),
+            relief="flat",
+            borderwidth=0,
+            background="#00000000",
+            activebackground="#00000000",
+            highlightthickness=0,
+            cursor="hand2",
+        )
+        btn.pack(side=tk.TOP, pady=12)
+        wrapper.pack_propagate(False)
+
     def _toolbar_palette(self) -> dict[str, str]:
         is_dark = getattr(self, "theme", "light") == "dark"
         if is_dark: