docs: add README badges and MIT license

[5000user5000]

Summary

Adds project metadata polish for the repository README and license information.

Changes

• Add README badges for:
  • React + Vite frontend
  • Spring Boot backend
  • PostgreSQL
  • SonarQube quality gate
  • 80%+ coverage
  • GCP + Grafana monitoring
  • MIT license
• Add a root LICENSE file using the MIT License.
• Add a README license section linking to the license file.

Validation

• Confirmed frontend coverage remains above 80%.
• Confirmed backend JaCoCo line coverage remains above 80%.
• Confirmed root SonarQube Quality Gate still passes.

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Project	Deployment	Actions	Updated (UTC)
cloud-native	Ready	Preview, Comment	May 30, 2026 10:45am

[5000user5000]

coverage 和 sonarQube 是靜態的
動態的話得等 repo 公開再說