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>

SPARC/config.py

@@ -12,3 +12,11 @@ api_key = os.getenv("API_KEY")
 
 # OpenRouter API key for LLM analysis
 openrouter_api_key = os.getenv("OPENROUTER_API_KEY")
+
+# Database configuration
+database_url = os.getenv("DATABASE_URL", "postgresql://postgres:postgres@localhost:5432/sparc")
+
+# Toggle between database mode and API mode
+# When True: stores all messages in database instead of sending to OpenRouter
+# When False: sends messages to OpenRouter API as normal
+use_database = os.getenv("USE_DATABASE", "false").lower() in ("true", "1", "yes")