Replace database-managed timestamps with Spring JPA auditing for created_at and updated_at fields

[coderabbitai]

Description

Currently, the file_info table uses database-managed timestamps with DEFAULT CURRENT_TIMESTAMP for both created_at and updated_at fields. However, the FileInfo entity already has Spring JPA auditing annotations (@CreatedDate and @LastModifiedDate) and @EnableJpaAuditing is configured.

Current State

• Database schema: created_at timestamp DEFAULT CURRENT_TIMESTAMP
• Database schema: updated_at timestamp DEFAULT CURRENT_TIMESTAMP
• Entity has @CreatedDate and @LastModifiedDate annotations
• @EnableJpaAuditing is enabled in WebMvcConfig

Desired State

• Remove DEFAULT CURRENT_TIMESTAMP from database schema
• Make both fields NOT NULL since Spring will guarantee their population
• Rely entirely on Spring JPA auditing for timestamp management

Benefits

• Consistent timestamp management at the application layer
• Better testability and control over audit fields
• Cleaner separation of concerns

Changes Required

1. Update init-db.sql to remove database defaults and add NOT NULL constraints
2. Ensure Spring auditing is properly configured (already done)
3. Update any existing data migration if needed

References

• PR: feat : apply encryption if enabled #914
• Comment: feat : apply encryption if enabled #914 (comment)
• Requested by: @rajadilipkolli