Fix race condition and add validation in user special membership request patch method

[Copilot]

Addresses review feedback from PR #667. The patch method had a race condition with async Celery calls, lacked input validation, and didn't maintain audit timestamps.

Changes

• Await Celery client call: Fixed race condition where test assertions could execute before task queueing completed. Changed from .catch() pattern to proper await with try-catch.

• Update dateLastModified: Automatically set on patch operations to maintain audit trail consistency with create operations.

• Validate status field: Reject invalid status values with BadRequest. Only pending, approved, rejected are permitted.

• Use Winston logger: Replaced console.error with logger.error for consistent log management.

// Before
await record.update(data)
if (this.celeryClient)
  this.celeryClient.run({ task: '...', args: [record.id] })
    .catch(err => console.error('Error:', err))

// After
const updateData = { ...data, dateLastModified: new Date() }
await record.update(updateData)
if (this.celeryClient) {
  try {
    await this.celeryClient.run({ task: '...', args: [record.id] })
  } catch (err) {
    logger.error('Error:', err)
  }
}

Added test coverage for status validation and dateLastModified behavior.

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