🐛 fix(gui): fix config save and UI freeze on startup

Config save fix:
- Add _sync_config_from_ui() to sync UI values to Config object
- Store _ip_string_var reference for IP field sync
- Call _sync_config_from_ui() before every save operation
- Fix _on_close to sync before saving

UI freeze fix:
- Defer _check_vitis() and _refresh_ports_initial() to _deferred_init()
- Use self.after(100, ...) to defer until window is displayed
- Window now appears immediately, blocking ops run in background

src/gui/main_window.py

@@ -80,15 +80,24 @@ class MainWindow(ctk.CTk):
         self._zynq_jtag_present: bool = False
         self._zynq_jtag_info = None
 
+        # StringVar references for config sync
+        self._ip_string_var: ctk.StringVar | None = None
+
         self._load_config()
         self._build_ui()
-        self._check_vitis()
-        self._refresh_ports_initial()
         self._update_step_dependencies()
 
         # Handle window close
         self.protocol("WM_DELETE_WINDOW", self._on_close)
 
+        # Defer blocking operations until after the window is displayed
+        self.after(100, self._deferred_init)
+
+    def _deferred_init(self) -> None:
+        """Run blocking operations after the window is shown."""
+        self._check_vitis()
+        self._refresh_ports_initial()
+
     # ── Config ─────────────────────────────────────────────────
 
     def _find_config(self) -> Path | None:
@@ -126,8 +135,29 @@ class MainWindow(ctk.CTk):
         else:
             self._config = Config.from_default()
 
+    def _sync_config_from_ui(self) -> None:
+        """Read current UI values and update the Config object.
+
+        This must be called before _save_config() to ensure
+        the Config object has the latest UI values.
+        """
+        if not self._config:
+            return
+        # Sync IP address
+        if self._ip_string_var:
+            self._config.zynq_ip = self._ip_string_var.get()
+        # Sync serial port
+        self._config.serial_port = self._port_var.get()
+        # Sync file paths from FileSelectors
+        files = self._get_selected_files()
+        self._config.bootloader_bit_path = files["bootloader_bit_path"]
+        self._config.bootloader_elf_path = files["bootloader_elf_path"]
+        self._config.bootloader_bin_path = files["bootloader_bin_path"]
+        self._config.firmware_bin_path = files["firmware_bin_path"]
+
     def _save_config(self) -> None:
         """Save current configuration to file."""
+        self._sync_config_from_ui()  # Sync UI values first
         if self._config and self._config.config_path:
             self._config.save()
 
@@ -335,7 +365,8 @@ class MainWindow(ctk.CTk):
         ip_frame.grid_columnconfigure(1, weight=1)
 
         ctk.CTkLabel(ip_frame, text="Zynq IP:", font=FONT_BODY).grid(row=0, column=0, sticky="w")
-        self._ip_entry = ctk.CTkEntry(ip_frame, textvariable=ctk.StringVar(value=self._config.zynq_ip))
+        self._ip_string_var = ctk.StringVar(value=self._config.zynq_ip)
+        self._ip_entry = ctk.CTkEntry(ip_frame, textvariable=self._ip_string_var)
         self._ip_entry.grid(row=0, column=1, sticky="nsew", padx=PADDING_SMALL)
 
         # BIT path (Bootloader)
@@ -946,6 +977,7 @@ class MainWindow(ctk.CTk):
     def _on_close(self) -> None:
         """Handle window close event: save config and cleanup."""
         if self._config:
+            self._sync_config_from_ui()  # Sync UI values first
             try:
                 self._config.save()
             except Exception: