🐛 fix(gui): make UART unavailable notification persistent

- Add dedicated UART warning label that doesn't get overwritten
- _show_uart_notification now uses persistent label instead of status display
- Warning message stays visible throughout workflow execution

src/gui/main_window.py

@@ -452,6 +452,19 @@ class MainWindow(ctk.CTk):
         self._status = StatusDisplay(panel)
         self._status.pack(fill="x", padx=PADDING, pady=PADDING)
 
+        # UART warning label (persistent, not overwritten by other status updates)
+        self._uart_warning_label = ctk.CTkLabel(
+            panel,
+            text="",
+            font=FONT_BODY,
+            anchor="w",
+            text_color=WARNING_COLOR,
+        )
+        self._uart_warning_label.pack(
+            fill="x", padx=PADDING, pady=(0, PADDING_SMALL)
+        )
+        self._uart_warning_label.pack_forget()  # Hide by default
+
     # ── Workflow Steps ─────────────────────────────────────────
 
     def _log_message(self, message: str) -> None:
@@ -562,13 +575,24 @@ class MainWindow(ctk.CTk):
         return True
 
     def _show_uart_notification(self, reason: str) -> None:
-        """Show a non-blocking UART unavailable notification in the status panel.
+        """Show a persistent UART unavailable notification.
+
+        This notification stays visible and is not overwritten by other status updates.
 
         Args:
             reason: Why UART is unavailable.
         """
-        msg = f"UART 不可用 ({reason})，日志分析及检查将禁用"
-        self.after(0, lambda: self._status.set_status(msg, "warning"))
+        msg = f"⚠ UART 不可用 ({reason})，日志分析及检查将禁用"
+        self.after(0, lambda: self._show_uart_warning(msg))
+
+    def _show_uart_warning(self, msg: str) -> None:
+        """Display the persistent UART warning message.
+
+        Args:
+            msg: Warning message to display.
+        """
+        self._uart_warning_label.configure(text=msg)
+        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."""