tech-debt: WorkerRepository missing operationErrorHandler

[dean0x]

Context

Greptile self-review comment on PR #94. Pre-existing pattern deviation, not introduced by the PR.

Problem

All other repositories use operationErrorHandler() from core/errors.js as the centralized error mapping function. WorkerRepository manually constructs BackbeatError inline in every method.

Note: register() has special UNIQUE constraint detection logic which may justify a custom error mapper for that one method. The other 6 methods should use operationErrorHandler.

Fix

Import and use operationErrorHandler for all methods except register().

[dean0x]

Already implemented — all 6 tryCatch() methods use operationErrorHandler(). register() has intentional custom error handling for UNIQUE constraint detection (Edge Case J).