fix: align OpenClaw plugin metadata

[vincentkoc]

Summary

• remove unsupported top-level OpenClaw manifest fields
• declare openclaw.compat.pluginApi / gateway compatibility metadata

Why

This PR comes from an OpenClaw core maintainer compatibility pass across Crabpot's visible plugin fixtures. The goal is to improve the overall OpenClaw plugin experience by helping widely used plugins clear high-signal Crabpot/plugin-inspector findings before they become install, ClawHub, or compatibility problems.

Relevant projects:

• OpenClaw: https://github.com/openclaw/openclaw
• Crabpot compatibility reports: https://github.com/openclaw/crabpot
• plugin-inspector: https://github.com/openclaw/plugin-inspector

Crabpot findings

Discovered in Crabpot at openclaw/crabpot@3b5131e345404e551ab09f6af686462fa8095ef2:

• manifest-unknown-fields: https://github.com/openclaw/crabpot/blob/3b5131e345404e551ab09f6af686462fa8095ef2/reports/crabpot-report.md#L1246-L1251
• package-plugin-api-compat-missing: https://github.com/openclaw/crabpot/blob/3b5131e345404e551ab09f6af686462fa8095ef2/reports/crabpot-report.md#L1252-L1257

Maintainer test instructions

You can verify this package with plugin-inspector from this repo:

npx @openclaw/plugin-inspector check --plugin-root . --openclaw /path/to/openclaw --json

For a local plugin-inspector checkout, use:

node /path/to/plugin-inspector/src/cli.js check --plugin-root . --openclaw /path/to/openclaw --json

Local validation

• JSON parse check for touched package/manifest files
• node /Users/vincentkoc/GIT/_Perso/plugin-inspector/src/cli.js check --plugin-root . --openclaw /Users/vincentkoc/GIT/_Perso/openclaw --json
• Local plugin-inspector result: pass, 0 plugin-owned residues after this patch

Remaining findings

Any remaining findings after this patch are owned by OpenClaw core or plugin-inspector capture/runtime coverage, not this plugin package metadata.