Backend: Escrow service decomposition into focused services

[KuchiMercy]

Summary

escrow.service.ts is 1,219 lines handling creation, funding, release, disputes, queries, and expiration in a single file. Decomposing this into focused services improves maintainability and makes all subsequent escrow feature work easier.

Requirements

• Split escrow.service.ts into focused service classes:
  • EscrowLifecycleService — create, cancel, expire, state transitions
  • EscrowFundingService — fund, release milestones, refund
  • EscrowDisputeService — file dispute, resolve dispute, evidence management
  • EscrowQueryService — findAll, findOne, findOverview, search, filter
• Maintain the existing EscrowController API surface (no breaking changes to endpoints)
• Extract shared validation logic into the existing EscrowStateMachine
• Update the escrow module to register all new services
• Ensure all existing tests still pass after decomposition

Acceptance Criteria

• escrow.service.ts is replaced by 4 focused service files
• No public API or endpoint changes (backward compatible)
• All existing unit tests pass without modification (or with minimal import path updates)
• Each new service file is under 400 lines
• Controller injects the appropriate service for each endpoint
• State machine validation is shared across services

Context

• Current service: apps/backend/src/modules/escrow/services/escrow.service.ts (1,219 lines)
• State machine: apps/backend/src/modules/escrow/escrow-state-machine.ts
• Controller: apps/backend/src/modules/escrow/escrow.controller.ts

Points: 150