feat: enrich identity conflict responses with member ids (CM-1349)

[skwowet]

Summary

Adds conflicting member ownership to public API identity 409 alerts and responses so ops and clients can see who already holds the identity.

Changes

• Look up conflictMemberId on verified-identity unique violations for create member, create identity, and verify identity
• Gate the lookup with isMemberIdentityDbConflict so non-conflict errors skip the extra query
• Move optional context onto HttpError so 409 responses include it in the JSON body
• Pass error.context through the public API error handler for Slack alerts

[Copilot]

Pull request overview

Enriches public API identity-conflict responses and Slack alerts with the member currently owning the verified identity.

Changes:

• Adds conflict detection and owner lookup across member identity operations.
• Adds optional context to all HTTP error responses.
• Passes HTTP error context to public API alerts.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
services/libs/common/src/errors/http.ts	Adds serialized HTTP error context.
backend/src/utils/err.ts	Adds identity-conflict detection.
backend/src/api/public/v1/members/createMember.ts	Looks up conflicting identity owner.
backend/src/api/public/v1/members/identities/createMemberIdentity.ts	Enriches creation conflicts.
backend/src/api/public/v1/members/identities/verifyMemberIdentity.ts	Enriches verification conflicts.
backend/src/api/public/middlewares/errorHandler.ts	Includes context in alerts.

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