refactor(runtime-host): centralize Node errno error guard

[seekskyworld]

Problem

Runtime Host currently defines the same isNodeError(error, code) guard in several independent modules. The copies are byte-level duplicates today, but some use a type predicate while others return boolean; the drift makes error handling harder to audit and encourages ad-hoc casts at filesystem boundaries.

Scope

• Add one Runtime Host-local Node errno guard with the existing conservative Error and exact-code semantics.
• Migrate control/endpoint.ts, operator/managed-deployment.ts, and peer-reachability/publisher.ts.
• Keep the control registration/startup and peer-mesh modules out of this PR because they are covered by an active Windows durability change.

Acceptance criteria

• The migrated modules have no local duplicate guard and preserve their current type narrowing and behavior for ENOENT, EPERM, and other codes.
• Non-Error values and mismatched codes continue to return false.
• A focused unit test pins the shared guard's type-predicate behavior.

This follows the parallel-helper finding in the repository audit and is intentionally limited to files without an active PR conflict.

[seekskyworld]

我认领这个 Runtime Host 切片。会提取保守的 Node errno type guard，迁移三个无活动 PR 冲突的模块，保留 exact-code 与 Error-only 语义，并加入 focused 单元测试。