v1.21.0

Changelog

• cf876ab Harden read-only protection: side-effect SELECTs and DB-layer enforcement (#77)
• e38d7ea ci: Codecov hardening and release smoke tests (#83)
• a8ebb78 feat(errors): structured error guidance for AI agents (#84)
• 0811bc1 feat(query): 查询结果行数上限与 schema include_system 修复 (#85)
• 8e71dd4 fix(db): reduce Sonar complexity and expand read-only unit tests (#81)
• 962f287 fix(mcp): require dual authorization for write queries (#76)
• a8f407d fix(web): redact secrets in config API and preserve on masked save (#75)
• a1cc4f0 fix: schema dump integration cleanup and webui npm audit (#80)
• b9b8022 refactor(mcp): reuse app layer and add schema discovery tools (#82)