fix: resolve DeepSeek tool_calls args parsing validation error

Added ToolCallArgsParsingWrapper to handle AI providers (like DeepSeek)
that return tool_calls.args as JSON strings instead of dictionaries.

The wrapper monkey-patches ChatOpenAI's _create_chat_result method to
parse string arguments before AIMessage construction, preventing
Pydantic validation errors.

Changes:
- New: agent/chat_model_wrapper.py - Wrapper implementation
- Modified: agent/base_agent/base_agent.py - Wrap model during init
- Modified: CHANGELOG.md - Document fix as v0.4.1
- New: tests/unit/test_chat_model_wrapper.py - Unit tests

Generated with [Claude Code](https://claude.com/claude-code)

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

agent/base_agent/base_agent.py

@@ -33,6 +33,7 @@ from tools.deployment_config import (
 from agent.context_injector import ContextInjector
 from agent.pnl_calculator import DailyPnLCalculator
 from agent.reasoning_summarizer import ReasoningSummarizer
+from agent.chat_model_wrapper import ToolCallArgsParsingWrapper
 
 # Load environment variables
 load_dotenv()
@@ -208,10 +209,10 @@ class BaseAgent:
             # Create AI model (mock in DEV mode, real in PROD mode)
             if is_dev_mode():
                 from agent.mock_provider import MockChatModel
-                self.model = MockChatModel(date="2025-01-01")  # Date will be updated per session
+                base_model = MockChatModel(date="2025-01-01")  # Date will be updated per session
                 print(f"🤖 Using MockChatModel (DEV mode)")
             else:
-                self.model = ChatOpenAI(
+                base_model = ChatOpenAI(
                     model=self.basemodel,
                     base_url=self.openai_base_url,
                     api_key=self.openai_api_key,
@@ -219,6 +220,10 @@ class BaseAgent:
                     timeout=30
                 )
                 print(f"🤖 Using {self.basemodel} (PROD mode)")
+
+            # Wrap model to fix tool_calls args parsing
+            self.model = ToolCallArgsParsingWrapper(model=base_model)
+            print(f"✅ Applied tool_calls args parsing wrapper")
         except Exception as e:
             raise RuntimeError(f"❌ Failed to initialize AI model: {e}")
 
@@ -541,7 +546,7 @@ Summary:"""
 
         # Update mock model date if in dev mode
         if is_dev_mode():
-            self.model.date = today_date
+            self.model.wrapped_model.date = today_date
 
         # Get job_id from context injector
         job_id = self.context_injector.job_id if self.context_injector else get_config_value("JOB_ID")