feat: integrate environment configuration into development workflow

- Auto-create .env file from template during setup-dev
- Add validate-config target to Makefile for configuration validation
- Update check-uv.sh to use environment variable for GitHub URL
- Provide helpful setup messages and next steps for developers

check-uv.sh

@@ -233,7 +233,7 @@ fi
 
 echo ""
 echo -e "${CYAN}For more information:${NC}"
-echo -e "  ${BLUE}UnitForge: https://github.com/unitforge/unitforge${NC}"
+echo -e "  ${BLUE}UnitForge: ${GITHUB_URL:-https://github.com/will666/unitforge}${NC}"
 echo -e "  ${BLUE}uv docs: https://github.com/astral-sh/uv${NC}"
 
 # Exit with appropriate code