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>

.env.example

@@ -0,0 +1,16 @@
+# SPARC Configuration
+
+# SerpAPI key for patent search
+API_KEY=your_serpapi_key_here
+
+# OpenRouter API key for LLM analysis
+OPENROUTER_API_KEY=your_openrouter_key_here
+
+# Database configuration (for docker-compose setup)
+DATABASE_URL=postgresql://postgres:postgres@localhost:5432/sparc
+
+# Toggle between database mode and API mode
+# When USE_DATABASE=true: stores all messages in database instead of sending to OpenRouter
+# When USE_DATABASE=false: sends messages to OpenRouter API as normal
+# Default: false
+USE_DATABASE=false