[Backend] Dynamic Off-Chain Refactoring `PATCH /goals/:id`

[Olowodarey]

Background & Context: People change their minds, delay vacations, and alter goals drastically without moving underlying vault configurations mathematically.
Description: Orchestrate mutation controls explicitly locking users explicitly to only their underlying mapping parameters preventing Cross-tenant attacks.
Acceptance Criteria:

• Require JwtAuthGuard.
• TypeORM findOne({ where: { id: params.id, userId: req.user.id } }) preventing IDOR modification mapping implicitly.
• Update fields allowing nullable clearing logic.
  Target Files: backend/src/modules/savings/savings.controller.ts.