refactor: register gateway executor checks and reuse payload normalization

[Qiyuanqiii]

Summary

Gateway executor requirements were maintained in a separate tool-name list, and argument validation repeated the payload-normalizer dispatch already held by the registry. Register the existing executor checks beside the tool definitions and reuse the registered normalizers.

Checks still run before budget charging. Browser calls select the existing Agent Browser or legacy executor from the payload version. Tool-specific identity, lease, operation-key, and live authority checks remain in place; remove the unreachable argument branch for retired host-command proposals.

Cleanup candidates were contributed by MiniMax-AI-Dev; the commit credits both MiniMax-AI-Dev and Codex.

Validation

• Passed go test ./internal/toolgateway (local Go 1.26.6), covering catalog membership, dispatch, protocol validation, authorization, and budget ordering.
• Added behavior cases for command/Docker/browser executor rejection before budget charging and preservation of the original WorkItem/Note title limit when redaction expands the text.
• CLI build passed. Full Go 1.25 and platform checks use the existing PR CI.

Surface governance

• No Surface is added, promoted, downgraded, deprecated, or removed.
• Registry item(s): N/A — no Surface change.
• Target tier / transition: N/A — no Surface change.
• Entry criteria / decision: N/A — no Surface change.
• Owner: N/A — no Surface change.
• Shared Go Application contract: Existing Tool Gateway and tool executor contracts.
• Authority impact: None; existing caller fences and authorization rules remain enforced.
• Supported platforms: Existing supported platforms, unchanged.
• Release / test evidence: Focused checks above and existing CI.
• Compatibility strategy: Keep tool names, payload formats, catalogs, and historical reader classifications.
• Deprecation window: N/A — no Surface change.
• Removal / rollback plan: Revert this source refactor; no persistence changes.

Audit

• No credentials or local runtime data are included.
• Policy, workspace, sandbox, and persistence boundaries were reviewed.
• Architecture status documents registration-owned preflight checks.