Remove legacy instance routes from the Blaze API

[WeissonHan]

Goal

Expose Blaze sandbox management through one HTTP namespace and remove the former instance-route compatibility surface.

Required behavior

Blaze must register only these sandbox lifecycle and guest-operation routes:

• GET /v1/sandboxes
• POST /v1/sandboxes
• GET /v1/sandboxes/{id}
• DELETE /v1/sandboxes/{id}
• POST /v1/sandboxes/{id}/exec
• POST /v1/sandboxes/{id}/read
• POST /v1/sandboxes/{id}/write

The former /v1/instances namespace must not be registered. Requests below it must return 404 Not Found without reading or changing sandbox lifecycle, runtime, or storage state.

Action-style reset, checkpoint, and destroy routes must not be registered under /v1/sandboxes. Canonical destruction remains DELETE /v1/sandboxes/{id}.

This route removal does not rename the existing JSON fields, including instance and instance_id, and does not change the successful sandbox routes' status codes or resource effects.

Checkpoint capture and checkpoint listing are delivered separately by #2444 and #2472.

Acceptance criteria

• Production routing contains no /v1/instances handler or compatibility adapter.
• The seven sandbox routes above use the existing lifecycle and guest-operation implementations.
• Tests prove that former instance routes and unregistered sandbox action routes return 404 without changing sandbox state.
• Tests cover successful sandbox create, list, get, exec, read, write, and delete operations.
• English and Chinese component documentation and user guidance describe the route removal and client migration.
• The component lifecycle design records the namespace and ownership boundary.
• No prerequisite pull request other than the current main branch is required for this route change.

Implemented by #2585.

[github-actions]

🔀 Issue Router

• Component: blaze
• Confidence: 99%
• Owners notified: @kongche-jbw
• No assignee was added; assignment records active implementation ownership.

问题涉及 Blaze daemon 的 sandbox 与 instance 路由兼容层。

Evidence: 标题明确标注 feat(blaze)，正文围绕 sandbox API 路由及其兼容适配展开。

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