✨ feat: collapsible flash sub-steps UI + erase_all checkbox

Rename erase_before_program → erase_all (semantics fix):
- erase_all: true  → -erase_all -erase_only (entire flash chip)
- erase_all: false → -erase_only (sectors matching BIN size)
Both options always erase; the checkbox controls scope, not yes/no.

UI additions:
- SubStepFrame widget: collapsible Erase/Program/Verify sub-steps
  with status dots (○/◉/●) and colored labels
- Automatically expands on Step 2 start, collapses on completion
- Phase and progress driven by real-time program_flash output parsing
- Checkbox label: '整片Flash擦除 (Erase entire flash)'

subprocess_utils.py phase detection:
- Parses 'Performing Erase/Program/Verify Operation' for phase transitions
- Emits 'phase' callbacks (erase/program/verify/done)
- Progress % tracked within current phase

src/config_manager.py

@@ -26,7 +26,7 @@ DEFAULT_CONFIG: dict[str, Any] = {
     "fsbl_elf_path": "",
     "flash_type": "qspi-x4-single",
     "flash_model": "s25fl256s1",
-    "erase_before_program": True,
+    "erase_all": False,
     "firmware_bin_path": "",
     "reboot_timeout": 30,
     "ping_timeout": 5,
@@ -63,7 +63,7 @@ class Config:
     fsbl_elf_path: str = ""
     flash_type: str = "qspi-x4-single"
     flash_model: str = "s25fl256s1"
-    erase_before_program: bool = True
+    erase_all: bool = False
     firmware_bin_path: str = ""
     reboot_timeout: int = 30
     ping_timeout: int = 5
@@ -171,7 +171,7 @@ class Config:
             "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,
+            "erase_all": self.erase_all,
             "firmware_bin_path": self._relative_path(self.firmware_bin_path),
             "reboot_timeout": self.reboot_timeout,
             "ping_timeout": self.ping_timeout,