[codex] Add account deletion release support

[jjoonleo]

Summary

• add a public /account-deletion HTML page for Google Play account deletion requirements
• allow the page through Spring Security and the custom JWT filter without login
• include backend retention cleanup support already present on dev for deletion feedback and API logs
• document the public URL, hosting surface, request channel, and retention enforcement boundaries

Validation

• ./gradlew test

Notes

• Outside-app account deletion requests are handled by email at jjoonleo@gmail.com.
• The Google Play URL is https://3.38.172.54.nip.io/account-deletion after the backend deploy reaches production.