refactor(ai_client): narrow bare 'except:' in _execute_tool_calls_concurrently (Phase 9 sites 6+7)

Both deepseek and minimax branches in the tool call dispatcher had:
  try: args = json.loads(tool_args_str)
  except: args = {}

json.JSONDecodeError is a subclass of ValueError, so narrowed to:
  except (ValueError, TypeError): args = {}

This satisfies the BC classification (specific exception types).

src/ai_client.py

@@ -713,14 +713,14 @@ async def _execute_tool_calls_concurrently(
    tool_args_str = cast(str, tool_info.get("arguments", "{}"))
    call_id       = cast(str, fc.get("id"))
    try: args     = json.loads(tool_args_str)
-   except: args = {}
+   except (ValueError, TypeError): args = {}
   elif provider == "minimax":
    tool_info     = fc.get("function", {})
    name          = cast(str, tool_info.get("name"))
    tool_args_str = cast(str, tool_info.get("arguments", "{}"))
    call_id       = cast(str, fc.get("id"))
    try: args     = json.loads(tool_args_str)
-   except: args = {}
+   except (ValueError, TypeError): args = {}
   else:
    continue