#523 - Replace DataManager dynamic usage with explicit dependencies

Parent: #523

## Objective
Reduce hidden coupling and improve testability by moving from dynamic DataManager usage to explicit dependencies in targeted paths.

## In scope
- Identify one or two high-traffic controllers/services using `new DataManager(...)`
- Replace with explicit repository/db dependency injection (module-level singleton or constructor-injected, based on repo conventions)
- Remove unused constructor argument patterns and tighten types where touched

## Acceptance criteria
- No new `new DataManager(config)` call sites introduced
- Selected paths use explicit dependencies instead of dynamic proxy behavior
- Tests updated to mock explicit boundaries
- Behavior remains backward-compatible

## Notes
Coordinate with the plan vertical-slice issue to avoid duplicate refactors.