fix: correct indentation of last_err in DeepSeekBrain.choose_action()

`last_err = None` was at module-level indentation (4 spaces) instead of
method-body indentation (8 spaces), causing an IndentationError on import.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/commander_ai_lab/sim/deepseek_brain.py

@@ -590,7 +590,7 @@ class DeepSeekBrain:
         if not self._connected:
             return self._fallback_action(snapshot, t_start, "not_connected")
 
-    last_err = None
+        last_err = None
         for attempt in range(1, self.config.max_retries + 1):
             try:
                 result = self._call_llm(snapshot)