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.

views/left_sidebar.py

@@ -0,0 +1,8 @@
+from tkinter import ttk
+
+
+class LeftSidebarView(ttk.LabelFrame):
+    def __init__(self, parent) -> None:
+        super().__init__(parent, text="Left Sidebar (Placeholder)")
+        ttk.Label(self, text="Layers / Assets / Tools").pack(anchor="nw", padx=10, pady=10)
+