Add Z.ai Coding Plan routing

[kywch]

Summary

• add explicit Z.ai Coding Plan provider, key, and endpoint routing
• reject registry-derived base URLs that do not match proxy protocol
• forward only validated generation parameters, using correct token field for Responses versus chat and native routes
• support current catalog entries and unlisted future GLM 5.x model IDs

Validation

• 296 focused tests passed
• Ruff, format, and git diff --check passed
• exact-head integration matrix completed all 10 selected arXiv conditions; OpenClaw and Claude ACP Z.ai conditions both earned reward 1
• full matrix had zero sandbox or trial errors; sole zero reward was unrelated Gemini provider 429

Review

This PR is intentionally stacked on #1030. After #1030 merges, retarget to main and verify final diff.

Maintainer or other-person review required. Author will not self-merge.

[devin-ai-integration]

Devin Review found 1 potential issue.

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[kywch]

Addressed endpoint-provenance finding: registry-generated provider env now carries explicit provenance, while user-supplied endpoints remain authoritative. Added direct, resolved-explicit, and registry-generated regressions. Refreshed onto #1030 head 5fbf930; all applicable CI checks pass.