feat: Implement initial Sprite Editor application with basic UI components

- Added main application class `SpriteEditorApp` with layout setup.
- Created menu bar with placeholder options.
- Implemented `BottomToolbarView`, `LeftSidebarView`, `MainEditorView`, `RightSidebarView` with basic UI elements.
- Added dialog classes for `ExportSettingsDialog` and `FlipbookCreatorDialog` to manage export settings and flipbook creation.
- Introduced support for loading and displaying images in the flipbook creator.
- Established a structure for handling sprite sheet composition and preview rendering.

sprite_editor.py

@@ -0,0 +1,66 @@
+import tkinter as tk
+from tkinter import ttk
+
+from views import (
+    BottomToolbarView,
+    FlipbookCreatorDialog,
+    LeftSidebarView,
+    MainEditorView,
+    RightSidebarView,
+    create_menu_bar,
+)
+
+
+class SpriteEditorApp:
+    def __init__(self, root: tk.Tk) -> None:
+        self.root = root
+        self.root.title("Sprite Editor (Placeholder)")
+        self.root.geometry("1200x750")
+
+        create_menu_bar(self.root, on_open_flipbook_creator=self._open_flipbook_creator)
+        self._create_layout()
+
+    def _create_layout(self) -> None:
+        container = ttk.Frame(self.root, padding=6)
+        container.pack(fill="both", expand=True)
+
+        vertical_panes = tk.PanedWindow(
+            container,
+            orient=tk.VERTICAL,
+            sashrelief=tk.RAISED,
+            sashwidth=6,
+        )
+        vertical_panes.pack(fill="both", expand=True)
+
+        horizontal_panes = tk.PanedWindow(
+            vertical_panes,
+            orient=tk.HORIZONTAL,
+            sashrelief=tk.RAISED,
+            sashwidth=6,
+        )
+
+        left_sidebar = LeftSidebarView(horizontal_panes)
+        main_editor = MainEditorView(horizontal_panes)
+        right_sidebar = RightSidebarView(horizontal_panes)
+        bottom_toolbar = BottomToolbarView(vertical_panes)
+
+        horizontal_panes.add(left_sidebar, minsize=160, width=220)
+        horizontal_panes.add(main_editor, minsize=400)
+        horizontal_panes.add(right_sidebar, minsize=160, width=220)
+
+        vertical_panes.add(horizontal_panes, minsize=280, stretch="always")
+        vertical_panes.add(bottom_toolbar, minsize=70, height=140)
+
+    def _open_flipbook_creator(self) -> None:
+        dialog = FlipbookCreatorDialog(self.root)
+        dialog.focus()
+
+
+def main() -> None:
+    root = tk.Tk()
+    SpriteEditorApp(root)
+    root.mainloop()
+
+
+if __name__ == "__main__":
+    main()