Add researcher profile API and identity linking

[jayvenn21]

Summary

• add a ResearcherProfile model for researcher-specific metadata attached to an existing Custos user
• add a ResearcherProfileStore interface and MySQL-backed store implementation
• add researcher_profiles database migration with a one-to-one relationship to users
• add service methods for researcher profile create/get/update/delete
• add REST endpoints and OpenAPI documentation for researcher profile management
• add a user identity link flow for external identities such as ORCID, CILogon, ACCESS, and NAIRR
• add integration tests for researcher profile round-trip behavior and ORCID-style identity linking
• remove the standalone SQL profile scaffold that used separate profiles, profile_emails, and external_identities tables

Notes

This aligns the researcher profile scaffold with the existing Custos identity model:

• users remains the stable Custos user identity
• user_identities remains the place for external identities such as ACCESS, NAIRR, CILogon, and ORCID
• researcher_profiles stores additional researcher metadata such as display name, research domain, research capabilities, department, and institution

Project memberships, group memberships, allocations, and publications are intentionally left out of this scaffold because they belong to separate relationship/domain models.

Validation

• gofmt -w pkg/models/profile.go internal/store/store.go internal/store/researcher_profile_store.go pkg/service/researcher_profile.go pkg/service/researcher_profile_integration_test.go pkg/service/integration_common_test.go internal/server/server.go
• go generate ./pkg/service/...
• go generate ./cmd/server
• go build ./...
• go vet ./...
• go test ./...
• go test -tags=integration ./pkg/service -run 'TestResearcherProfileRoundTrip|TestLinkUserIdentityLinksORCIDToExistingUser'
• git diff --check