✨ 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/gui/widgets.py

@@ -623,3 +623,135 @@ class LogDisplay(ctk.CTkFrame):
         self._text_widget.delete("1.0", "end")
         self._text_widget.insert("1.0", text)
         self._text_widget.configure(state="disabled")
+
+
+# ════════════════════════════════════════════════════════════════════
+# SubStepFrame — collapsible sub-step progress display
+# ════════════════════════════════════════════════════════════════════
+
+
+class SubStepFrame(ctk.CTkFrame):
+    """Collapsible frame showing flash operation sub-steps with status.
+
+    Three sub-steps: Erase → Program → Verify.
+    Each shows a status indicator (dot + label) updated via set_phase().
+    Collapsed by default, expands when a workflow step starts.
+    """
+
+    def __init__(self, parent: ctk.CTkFrame) -> None:
+        """Initialize the sub-step frame.
+
+        Args:
+            parent: Parent CTkFrame widget.
+        """
+        super().__init__(parent, fg_color="transparent")
+        self.grid_columnconfigure(1, weight=1)
+
+        # Collapse toggle
+        self._collapsed = True
+        self._toggle_btn = ctk.CTkButton(
+            self,
+            text="▶",
+            width=24,
+            height=24,
+            font=FONT_SMALL,
+            command=self._toggle,
+        )
+        self._toggle_btn.grid(row=0, column=0, padx=(PADDING_SMALL, 4), pady=(2, 0), sticky="nw")
+
+        self._header_label = ctk.CTkLabel(
+            self,
+            text="Sub-steps",
+            font=FONT_SMALL,
+        )
+        self._header_label.grid(row=0, column=1, padx=(0, PADDING), pady=(2, 0), sticky="w")
+
+        # Sub-items (hidden initially)
+        self._sub_items: list[dict] = []
+        sub_names = ["Erase", "Program", "Verify"]
+        for i, name in enumerate(sub_names):
+            dot = ctk.CTkLabel(self, text="○", font=(FONT_SMALL[0], 10), text_color=CONNECTOR_COLOR)
+            label = ctk.CTkLabel(self, text=name, font=FONT_SMALL, text_color=CONNECTOR_COLOR)
+            dot.grid(row=i + 1, column=0, padx=(PADDING_SMALL + 14, 4), pady=(1, 1), sticky="e")
+            label.grid(row=i + 1, column=1, padx=(4, PADDING), pady=(1, 1), sticky="w")
+            dot.grid_remove()
+            label.grid_remove()
+            self._sub_items.append({"dot": dot, "label": label, "name": name})
+
+    def _toggle(self) -> None:
+        """Toggle collapse/expand."""
+        self._collapsed = not self._collapsed
+        self._toggle_btn.configure(text="▶" if self._collapsed else "▼")
+        for item in self._sub_items:
+            if self._collapsed:
+                item["dot"].grid_remove()
+                item["label"].grid_remove()
+            else:
+                item["dot"].grid()
+                item["label"].grid()
+
+    def set_expanded(self, expanded: bool) -> None:
+        """Set expanded state.
+
+        Args:
+            expanded: True to expand, False to collapse.
+        """
+        if expanded == self._collapsed:
+            self._toggle()
+
+    def set_phase(self, phase: str, pct: int = -1) -> None:
+        """Update a sub-step's status.
+
+        Args:
+            phase: One of 'erase', 'program', 'verify', 'done'.
+            pct: Progress percentage, -1 to show "running", 100 for "done".
+        """
+        phase_map = {"erase": 0, "program": 1, "verify": 2}
+        colors = {
+            "pending": CONNECTOR_COLOR,
+            "running": PRIMARY_COLOR,
+            "complete": SUCCESS_COLOR,
+            "error": DANGER_COLOR,
+        }
+
+        if phase == "done":
+            # Mark all as complete
+            for item in self._sub_items:
+                item["dot"].configure(text="●", text_color=SUCCESS_COLOR)
+                item["label"].configure(text_color=SUCCESS_COLOR)
+            return
+
+        idx = phase_map.get(phase, -1)
+        if idx < 0:
+            return
+
+        # Determine state
+        if pct >= 100:
+            state = "complete"
+            dot_text = "●"
+        elif pct >= 0:
+            state = "running"
+            dot_text = "◉"
+        else:
+            state = "running"
+            dot_text = "◉"
+
+        # Update current and previous
+        for i, item in enumerate(self._sub_items):
+            if i < idx:
+                item["dot"].configure(text="●", text_color=SUCCESS_COLOR)
+                item["label"].configure(text_color=SUCCESS_COLOR)
+            elif i == idx:
+                item["dot"].configure(text=dot_text, text_color=colors[state])
+                item["label"].configure(text_color=colors[state])
+            else:
+                item["dot"].configure(text="○", text_color=colors["pending"])
+                item["label"].configure(text_color=colors["pending"])
+
+    def reset(self) -> None:
+        """Reset all sub-steps to pending state."""
+        for item in self._sub_items:
+            item["dot"].configure(text="○", text_color=CONNECTOR_COLOR)
+            item["label"].configure(text_color=CONNECTOR_COLOR)
+        if not self._collapsed:
+            self._toggle()