♻️ refactor(toolchain): replace impact/bootgen with xsct/program_flash + add fsbl

BREAKING: Replaces obsolete impact (ISE-era) and misused bootgen with
the correct Xilinx 2018.3–2023.2 toolchain.

Toolchain changes:
- vitis_checker: impact → xsct + program_flash + bootgen detection
- flash_programmer: bootgen/impact → program_flash (erase + program + verify)
- bitstream_programmer: impact → xsct fpga/dow (primary), vivado (fallback)
- Removed duplicated _get_impact_path() — now shared from vitis_checker

Config additions:
- fsbl_elf_path: FSBL ELF required by program_flash for QSPI init
- flash_type: QSPI mode (default: qspi-x4-single)

GUI additions:
- FSBL ELF file selector in Configuration panel
- Step 2 validates FSBL ELF is selected
- Step 1 now shows xsct/program_flash/bootgen in tool check

src/gui/main_window.py

@@ -184,6 +184,7 @@ class MainWindow(ctk.CTk):
         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.fsbl_elf_path = files["fsbl_elf_path"]
         self._config.firmware_bin_path = files["firmware_bin_path"]
 
     def _save_config(self) -> None:
@@ -396,7 +397,7 @@ class MainWindow(ctk.CTk):
             row=0, column=0, sticky="nsew",
             padx=PADDING, pady=PADDING,
         )
-        panel.grid_rowconfigure(5, weight=1)
+        panel.grid_rowconfigure(6, weight=1)
 
         title = ctk.CTkLabel(
             panel,
@@ -448,6 +449,17 @@ class MainWindow(ctk.CTk):
             self._bootloader_bin_selector.set_path(str(resolved))
         self._bootloader_bin_selector.grid(row=4, column=0, sticky="nsew", padx=PADDING, pady=PADDING_SMALL)
 
+        # FSBL ELF path (required by program_flash for QSPI programming)
+        self._fsbl_selector = FileSelector(
+            panel,
+            label_text="FSBL ELF (.elf):",
+            file_types=[("ELF files", "*.elf"), ("All files", "*")],
+        )
+        if self._config.fsbl_elf_path:
+            resolved = self._config.resolve_path(self._config.fsbl_elf_path)
+            self._fsbl_selector.set_path(str(resolved))
+        self._fsbl_selector.grid(row=5, column=0, sticky="nsew", padx=PADDING, pady=PADDING_SMALL)
+
         # Firmware BIN path (TFTP upload)
         self._firmware_bin_selector = FileSelector(
             panel,
@@ -457,7 +469,7 @@ class MainWindow(ctk.CTk):
         if self._config.firmware_bin_path:
             resolved = self._config.resolve_path(self._config.firmware_bin_path)
             self._firmware_bin_selector.set_path(str(resolved))
-        self._firmware_bin_selector.grid(row=5, column=0, sticky="nsew", padx=PADDING, pady=PADDING_SMALL)
+        self._firmware_bin_selector.grid(row=6, column=0, sticky="nsew", padx=PADDING, pady=PADDING_SMALL)
 
         # Save button
         save_btn = ctk.CTkButton(
@@ -466,7 +478,7 @@ class MainWindow(ctk.CTk):
             font=FONT_SMALL,
             command=self._save_config,
         )
-        save_btn.grid(row=6, column=0, padx=PADDING, pady=PADDING)
+        save_btn.grid(row=7, column=0, padx=PADDING, pady=PADDING)
 
     def _build_serial_panel(self, parent: ctk.CTkFrame) -> None:
         """Build the serial monitor panel."""
@@ -571,12 +583,13 @@ class MainWindow(ctk.CTk):
         """Get selected file paths from the UI.
 
         Returns:
-            Dictionary with bootloader_bit_path, bootloader_elf_path, bootloader_bin_path, firmware_bin_path.
+            Dictionary with all file paths from UI selectors.
         """
         return {
             "bootloader_bit_path": self._bit_selector.get_path(),
             "bootloader_elf_path": self._elf_selector.get_path(),
             "bootloader_bin_path": self._bootloader_bin_selector.get_path(),
+            "fsbl_elf_path": self._fsbl_selector.get_path(),
             "firmware_bin_path": self._firmware_bin_selector.get_path(),
         }
 
@@ -681,7 +694,7 @@ class MainWindow(ctk.CTk):
         self._uart_warning_label.pack(fill="x", padx=PADDING, pady=(0, PADDING_SMALL))
 
     def _run_step_2_program_flash(self) -> bool:
-        """Step 2: Program and verify Flash."""
+        """Step 2: Program and verify Flash using program_flash."""
         if not self._config:
             return False
 
@@ -690,7 +703,12 @@ class MainWindow(ctk.CTk):
             self._log_message("  No Bootloader BIN file selected")
             return False
 
+        if not files["fsbl_elf_path"]:
+            self._log_message("  No FSBL ELF file selected (required by program_flash)")
+            return False
+
         self._log_message(f"Step 2: Programming Flash with {files['bootloader_bin_path']}...")
+        self._log_message(f"  FSBL: {files['fsbl_elf_path']}")
 
         try:
             bin_path = Path(files["bootloader_bin_path"])