fix: reload tools after context injection and prevent database locking

Critical fixes for ContextInjector and database concurrency:

1. ContextInjector Not Working:
   - Made set_context() async to reload tools after recreating MCP client
   - Tools from old client (without interceptor) were still being used
   - Now tools are reloaded from new client with interceptor active
   - This ensures buy/sell calls properly receive injected parameters

2. Database Locking:
   - Closed main connection before _write_results_to_db() opens new one
   - SQLite doesn't handle concurrent write connections well
   - Prevents "database is locked" error during position writes

Changes:
- agent/base_agent/base_agent.py:
  - async def set_context() instead of def set_context()
  - Added: self.tools = await self.client.get_tools()
- api/model_day_executor.py:
  - await agent.set_context(context_injector)
  - conn.close() before _write_results_to_db()

Root Cause:
When recreating the MCP client with tool_interceptors, the old tools
were still cached in self.tools and being passed to the AI agent.
The interceptor was never invoked, so job_id/signature/date were missing.

api/model_day_executor.py

@@ -140,7 +140,7 @@ class ModelDayExecutor:
                 job_id=self.job_id,
                 session_id=session_id
             )
-            agent.set_context(context_injector)
+            await agent.set_context(context_injector)
 
             # Run trading session
             logger.info(f"Running trading session for {self.model_sig} on {self.date}")
@@ -155,10 +155,13 @@ class ModelDayExecutor:
             # Update session summary
             await self._update_session_summary(cursor, session_id, conversation, agent)
 
-            # Store positions (pass session_id)
-            self._write_results_to_db(agent, session_id)
-
+            # Commit and close connection before _write_results_to_db opens a new one
             conn.commit()
+            conn.close()
+            conn = None  # Mark as closed
+
+            # Store positions (pass session_id) - this opens its own connection
+            self._write_results_to_db(agent, session_id)
 
             # Update status to completed
             self.job_manager.update_job_detail_status(