feat: implement reasoning logs API with database-only storage

Complete implementation of reasoning logs retrieval system that
replaces JSONL file-based logging with database-only storage.

Database Changes:
- Add trading_sessions table (one record per model-day)
- Add reasoning_logs table (conversation history with summaries)
- Add session_id column to positions table
- Add indexes for query performance

Agent Changes:
- Add conversation history tracking to BaseAgent
- Add AI-powered summary generation using same model
- Remove JSONL logging code (_log_message, _setup_logging)
- Preserve in-memory conversation tracking

ModelDayExecutor Changes:
- Create trading session at start of execution
- Store reasoning logs with AI-generated summaries
- Update session summary after completion
- Link positions to sessions via session_id

API Changes:
- Add GET /reasoning endpoint with filters (job_id, date, model)
- Support include_full_conversation parameter
- Return both summaries and full conversation on demand
- Include deployment mode info in responses

Documentation:
- Add complete API reference for GET /reasoning
- Add design document with architecture details
- Add implementation guide with step-by-step tasks
- Update Python and TypeScript client examples

Testing:
- Add 6 tests for conversation history tracking
- Add 4 tests for summary generation
- Add 5 tests for model_day_executor integration
- Add 8 tests for GET /reasoning endpoint
- Add 9 integration tests for E2E flow
- Update existing tests for schema changes

All 32 new feature tests passing. Total: 285 tests passing.

tests/unit/test_database.py

@@ -90,7 +90,7 @@ class TestSchemaInitialization:
     """Test database schema initialization."""
 
     def test_initialize_database_creates_all_tables(self, clean_db):
-        """Should create all 9 tables."""
+        """Should create all 10 tables."""
         conn = get_db_connection(clean_db)
         cursor = conn.cursor()
 
@@ -112,7 +112,8 @@ class TestSchemaInitialization:
             'tool_usage',
             'price_data',
             'price_data_coverage',
-            'simulation_runs'
+            'simulation_runs',
+            'trading_sessions'  # Added in reasoning logs feature
         ]
 
         assert sorted(tables) == sorted(expected_tables)
@@ -192,9 +193,15 @@ class TestSchemaInitialization:
             'idx_positions_model',
             'idx_positions_date_model',
             'idx_positions_unique',
+            'idx_positions_session_id',  # Link positions to trading sessions
             'idx_holdings_position_id',
             'idx_holdings_symbol',
-            'idx_reasoning_logs_job_date_model',
+            'idx_sessions_job_id',  # Trading sessions indexes
+            'idx_sessions_date',
+            'idx_sessions_model',
+            'idx_sessions_unique',
+            'idx_reasoning_logs_session_id',  # Reasoning logs now linked to sessions
+            'idx_reasoning_logs_unique',
             'idx_tool_usage_job_date_model'
         ]
 
@@ -371,7 +378,7 @@ class TestUtilityFunctions:
         conn = get_db_connection(test_db_path)
         cursor = conn.cursor()
         cursor.execute("SELECT COUNT(*) FROM sqlite_master WHERE type='table' AND name NOT LIKE 'sqlite_%'")
-        assert cursor.fetchone()[0] == 9  # Updated to reflect all tables
+        assert cursor.fetchone()[0] == 10  # Updated to reflect all tables including trading_sessions
         conn.close()
 
         # Drop all tables