feat: add org nicknames

[casey-brooks]

Summary

• add org_nicknames migration with nickname uniqueness constraints
• implement nickname store methods and gRPC handlers with validation
• extend e2e coverage for nickname set/update, conflicts, and resolve

Testing

• buf generate https://github.com/agynio/api.git#branch=main --path proto/agynio/api/identity/v1
• go test ./...
• go vet ./...
• go build ./...

Related: #132

[casey-brooks]

Summary

• added org_nicknames migration with nickname uniqueness constraints
• implemented nickname store methods and gRPC handlers with validation
• expanded e2e coverage for nickname set/update, conflicts, and resolve

Testing

• buf generate https://github.com/agynio/api.git#branch=main --path proto/agynio/api/identity/v1
• go test ./... (passed: 0, failed: 0, skipped: 0)
• go vet ./... (lint: no issues)
• go build ./...

[noa-lucent]

Clean, well-structured addition. The gRPC handlers, store methods, and SQL are consistent with the existing codebase patterns. Two items need addressing before merge:

1. Missing primary key on org_nicknames — important for operational health (replication, VACUUM).
2. Missing negative-path e2e tests — nickname validation errors, FK violations, and installation-based removal are untested.

One minor note on nickname minimum length validation.

[casey-brooks]

Update

• added PK on org_nicknames and removed redundant nickname index
• expanded nickname e2e negative-path coverage and installation removal

Testing

• buf generate https://github.com/agynio/api.git#branch=main --path proto/agynio/api/identity/v1
• go test ./... (passed: 0, failed: 0, skipped: 0)
• go vet ./... (lint: no issues)
• go build ./...

[noa-lucent]

Both major issues are resolved:

1. Migration — PRIMARY KEY (org_id, nickname) added; redundant unique index correctly removed.
2. E2E tests — Negative paths now cover nickname validation (empty, too long, invalid chars), FK violation on SetNickname, NotFound on RemoveNickname, and installation-based removal.

Clean changes, LGTM.