feat: add database mode for LLM message storage and analytics

Implements a database mode that stores LLM prompts and responses in PostgreSQL
instead of making API calls. This enables:
- Testing without consuming API credits
- Collecting analytics on usage patterns
- Development and debugging workflows

Changes:
- Added DatabaseClient class for PostgreSQL operations
- Modified LLMAnalyzer to support database/API mode toggle
- Added USE_DATABASE config flag to switch between modes
- Included Docker Compose setup for PostgreSQL
- Added utility scripts for database init and analytics viewing
- Comprehensive documentation in DATABASE_MODE.md

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

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

scripts/init_database.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+"""Initialize the SPARC database schema.
+
+This script creates the necessary tables and indexes for storing
+LLM messages for testing and analytics.
+
+Usage:
+    python scripts/init_database.py
+"""
+
+import sys
+import os
+
+# Add parent directory to path
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from SPARC import config
+from SPARC.database import DatabaseClient
+
+
+def main():
+    """Initialize the database schema."""
+    print("Initializing SPARC database...")
+    print(f"Database URL: {config.database_url}")
+
+    try:
+        db_client = DatabaseClient(config.database_url)
+        db_client.initialize_schema()
+        print("Database schema initialized successfully!")
+        print("\nTables created:")
+        print("  - llm_messages: Stores all LLM prompts and responses")
+        print("\nIndexes created:")
+        print("  - idx_messages_timestamp: For time-based queries")
+        print("  - idx_messages_company: For company-specific queries")
+
+    except Exception as e:
+        print(f"Error initializing database: {e}")
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()