#523 - Reduce any usage in db2 model/query layer

[brijesh-amin]

Parent: #523

Objective

Improve data-layer correctness by reducing broad any usage and introducing stronger query/model typings.

In scope

• Start with high-traffic entities (e.g., plan/user) in db2 model/query paths
• Add typed DTO/query result contracts for selected models
• Refactor shared model base utilities where needed to support stronger typing

Acceptance criteria

• Measurable reduction of any in touched db2 files
• Typed create/update/find paths for selected entities
• No query behavior regressions in existing tests
• Additional tests for edge cases introduced by typing changes

Notes

Deliver incrementally to avoid high-risk all-at-once migration.