RED phase of TDD task 02-01-01. Locks the wire-format contract for
GET /api/v1/me before the DTO exists:
- camelCase JSON keys (id, sub, email, displayName) per D-27
- ignoreUnknownKeys forward compat for Phase 3 householdId per D-28
- MeResponse.toUser() one-to-one mapping
Wires kotlinx.serialization into shared/build.gradle.kts (api scope so
both client and server inherit the @Serializable runtime) and adds the
kotlinx-serializationJson catalog alias. The shared module remains
pure: only kotlin stdlib + kotlinx.serialization-json are pulled into
commonMain (D-19 / INFRA-06 still holds).
Test currently fails: MeResponse and User unresolved; GREEN follows.
