[BUG] Independent bootstrap heartbeat reports a payload key as the instance type #7696

Current behavior

HeartbeatListener sets instanceType to InstanceTypeConstants.BOOTSTRAP_INSTANCE_INFO (bootstrapInstanceInfo) rather than BOOTSTRAP_INSTANCE_TYPE (bootstrap). The WebSocket and HTTP-sync listeners use bootstrap. Admin includes instance type in the identity key and filters instances by type, so the independent reporting channel can produce a differently classified instance or a second identity when reporting modes change.

Acceptance criteria

• Independent heartbeats use the canonical bootstrap instance type.
• Test DTOs emitted by the heartbeat listener and Admin filtering/identity across all reporting channels.
• Define treatment of existing legacy bootstrapInstanceInfo rows without merging distinct namespaces or addresses.
• Document and test compatibility when switching reporting mode; retain the payload-key constant for its intended use.

Source evidence

Reviewed source. Baseline: b4e115367fd57adc8aba332d655b1009932ba394. Report based on source inspection; no runtime reproduction was executed during issue preparation.