Define machine_ingestion schema

[ianderson-nvidia]

Summary

Define and document the protobuf/model boundary for machine attributes that are established at ingestion or through ExpectedMachine, but are not mutable operator configuration and are not observed runtime status.

Evaluate introducing a dedicated static_config or ingestion_config section on forge.Machine

Rationale

MachineConfig should represent operator-mutable values changed through mutating APIs and tracked by the machine configuration version. MachineStatus should represent observed/runtime state. Some machine attributes are established during ingestion and may be immutable afterward, so neither category accurately describes them.

Affected areas

• crates/rpc/proto/forge.proto: forge.Machine, forge.MachineConfig, and forge.MachineStatus
• rest-api/proto/core/src/v1/nico_nico.proto, if it mirrors the Forge machine schema
• crates/api-model/src/machine/ and RPC conversion code
• Style-guide/config-status guidance, if applicable

Context

Requested by @ianderson-nvidia following the design discussion in #2847.

• PR: refactor(machine): separate Machine fields into config/status #2847
• Discussion: refactor(machine): separate Machine fields into config/status #2847 (comment)