✨ feat(uart): add UART availability check, inter-step delays, and post-download Zynq status verification

- Add check_uart_available() to serial_monitor.py — detects port availability
- Add verify_zynq_status() to boot_verifier.py — lightweight post-download check
- Add uart_delay / inter_step_delay config fields (defaults: 3s / 2s)
- Step 1: Check UART availability, show non-blocking 'UART 不可用' notification
- Step 4: Add post-download Zynq status check (ping + serial) after TFTP
- _run_steps_worker: Add configurable inter-step delays between all steps
- Update step labels (4a→4b→4c→4d) for clarity

src/config_manager.py

@@ -27,6 +27,8 @@ DEFAULT_CONFIG: dict[str, Any] = {
     "reboot_timeout": 30,
     "ping_timeout": 5,
     "ping_count": 3,
+    "uart_delay": 3,
+    "inter_step_delay": 2,
 }
 
 
@@ -50,6 +52,8 @@ class Config:
     reboot_timeout: int = 30
     ping_timeout: int = 5
     ping_count: int = 3
+    uart_delay: int = 3
+    inter_step_delay: int = 2
 
     # Internal: path to the config file on disk
     _config_path: Path = field(default=None, init=False, repr=False)
@@ -151,6 +155,8 @@ class Config:
             "reboot_timeout": self.reboot_timeout,
             "ping_timeout": self.ping_timeout,
             "ping_count": self.ping_count,
+            "uart_delay": self.uart_delay,
+            "inter_step_delay": self.inter_step_delay,
         }
         return data