✨ feat: flash phase tracking, erase checkbox, flash_model config

Step 2 UI now shows real-time flash operation phases parsed from program_flash output:
- Erase: "Performing Erase Operation..." → sf erase → Erased: OK
- Program: "Performing Program Operation..." → write blocks 0%→100%
- Verify: "Performing Verify Operation..." → read+cmp 0%→100%

Configuration additions:
- erase_before_program checkbox: controls whether to pre-erase before programming
- flash_model: chip type for capacity reference (s25fl256s1 = 32 MiB)

subprocess_utils.py now emits 'phase' callbacks (erase/program/verify/done)
detected from program_flash output transitions.

src/config_manager.py

@@ -25,6 +25,8 @@ DEFAULT_CONFIG: dict[str, Any] = {
     "bootloader_bin_path": "",
     "fsbl_elf_path": "",
     "flash_type": "qspi-x4-single",
+    "flash_model": "s25fl256s1",
+    "erase_before_program": True,
     "firmware_bin_path": "",
     "reboot_timeout": 30,
     "ping_timeout": 5,
@@ -60,6 +62,8 @@ class Config:
     bootloader_bin_path: str = ""
     fsbl_elf_path: str = ""
     flash_type: str = "qspi-x4-single"
+    flash_model: str = "s25fl256s1"
+    erase_before_program: bool = True
     firmware_bin_path: str = ""
     reboot_timeout: int = 30
     ping_timeout: int = 5
@@ -166,6 +170,8 @@ class Config:
             "bootloader_bin_path": self._relative_path(self.bootloader_bin_path),
             "fsbl_elf_path": self._relative_path(self.fsbl_elf_path),
             "flash_type": self.flash_type,
+            "flash_model": self.flash_model,
+            "erase_before_program": self.erase_before_program,
             "firmware_bin_path": self._relative_path(self.firmware_bin_path),
             "reboot_timeout": self.reboot_timeout,
             "ping_timeout": self.ping_timeout,