core: simplify account repo/service after review

- persistToken: positional params → named object to prevent swaps
- persistAccount: wrap in Database.transaction for atomicity
- Internal response schemas: Schema.Class → Schema.Struct (lighter)
- fromRow: pass row directly to decoder (strips unknown keys)
- Test: add afterAll runtime disposal, use branded ID in assertion

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>