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>

docker-compose.yml

@@ -0,0 +1,36 @@
+services:
+  postgres:
+    image: postgres:16-alpine
+    container_name: sparc-postgres
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_DB: sparc
+    ports:
+      - "5432:5432"
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+  app:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: sparc-app
+    depends_on:
+      postgres:
+        condition: service_healthy
+    environment:
+      USE_DATABASE: true
+      DATABASE_URL: postgresql://postgres:postgres@postgres:5432/sparc
+    ports:
+      - "8000:8000"
+    volumes:
+      - .:/app
+
+volumes:
+  postgres_data: