✨ feat: add scrollbar via CTkScrollableFrame for window resize

- Replace main_frame CTkFrame → CTkScrollableFrame for vertical scrollbar
- Remove main_frame.grid_rowconfigure weight — content natural height
- Remove right_frame.grid_rowconfigure weight — prevents squashing
- Left column (workflow + log) retains weight=1 for dominant width
- Right column (config/serial/utility/status) keeps natural narrow width

src/gui/main_window.py

@@ -265,10 +265,9 @@ class MainWindow(ctk.CTk):
 
     def _build_ui(self) -> None:
         """Build the complete UI layout."""
-        # Main container with padding
-        main_frame = ctk.CTkFrame(self)
+        # Scrollable main container — scrollbar appears when content overflows
+        main_frame = ctk.CTkScrollableFrame(self)
         main_frame.pack(fill="both", expand=True, padx=PADDING_LARGE, pady=PADDING_LARGE)
-        main_frame.grid_rowconfigure(1, weight=1)
         main_frame.grid_columnconfigure(0, weight=1)
 
         # ── Header ──
@@ -286,7 +285,6 @@ class MainWindow(ctk.CTk):
         # ── Right Panel: Configuration ──
         right_frame = ctk.CTkFrame(main_frame)
         right_frame.grid(row=1, column=1, sticky="nsew", padx=(PADDING, 0))
-        right_frame.grid_rowconfigure(3, weight=1)
         right_frame.grid_columnconfigure(0, weight=1)
 
         self._build_config_panel(right_frame)