fix: improve error handling and code robustness

- state_machine.rs: if-let replaces is_some()+take().unwrap()
- state_machine.rs: expect() replaces unwrap() with invariant docs
- wifi/mod.rs: send_result uses self.id() instead of hardcoded string

src/plugins/video/state_machine.rs

@@ -51,8 +51,7 @@ impl StateMachine {
         }
 
         // 有待执行的触发器时，跳过 sequence 剩余 step，立即切换状态
-        if self.pending_trigger_target.is_some() {
-            let target_state = self.pending_trigger_target.take().unwrap();
+        if let Some(target_state) = self.pending_trigger_target.take() {
             self.transition_to_state(&target_state)?;
             return Ok(self.current_state != old_state);
         }
@@ -273,7 +272,8 @@ impl StateMachine {
             }
         }
 
-        Ok(free_states.last().unwrap().0.clone())
+        // free_states 非空已由上方 bail! 保证
+        Ok(free_states.last().expect("free_states is non-empty").0.clone())
     }
 
     fn select_weighted_next_state(&self, entries: &[NextStateEntry]) -> Option<String> {

src/plugins/wifi/mod.rs

@@ -111,7 +111,7 @@ impl WifiPlugin {
             .context("wifi plugin context is not initialized")?;
 
         ctx.tx.send(Envelope {
-            from: "wifi".to_string(),
+            from: self.id().to_string(),
             to: Destination::Broadcast,
             message: Message::WifiResult(payload),
         })?;