[Maintainability] Consolidate redundant global constants

[JoelA510]

Status: Pending
Location: src/app/constants/index.js
Violation: Some constants are duplicated in feature-specific files.
Fix: Consolidate all global business constants into a single source of truth.

[JoelA510]

Partial resolution: Commit 2d3b607 (2026-02-26, branch feat/refactor-sprint-wave-15) extracted ROLES and POSITION_STEP from app/constants/index.js into a new src/shared/constants/index.ts. The app/constants/index.js now re-exports from shared/constants/ for backward compatibility. This resolves the FSD violation where shared/ was importing from app/constants/.

Remaining: the other app-layer constants (TASK_ORIGIN, TASK_STATUS, PROJECT_STATUS, STORAGE_BUCKETS) are still defined in app/constants/index.js. Consider whether any feature-specific files duplicate these.