Remove openclaw metadata from skills #269

Problem

The SKILL.md files in /skills/ include openclaw metadata in their YAML frontmatter:

metadata:
  openclaw:
    category: "productivity"
    requires:
      bins: ["gws"]
    cliHelp: "gws calendar --help"

This appears across all skills (gws-calendar, gws-gmail, gws-drive, etc.).

Why this is problematic

1. Vendor lock-in on an open format — Agent skills are just markdown files with YAML frontmatter. Introducing a third-party registry standard (openclaw) as metadata creates an unnecessary dependency on an external specification that doesn't govern how skills are consumed.

2. Skills should be tool-agnostic — The name, version, and description fields in the frontmatter are sufficient. Categorization and binary requirements can be expressed without adopting an external standard.

3. Confusion for contributors — Developers looking at these skills may assume openclaw is a required part of the skill format, when it has no effect on how Claude Code (or any other AI coding agent) processes the skill.

Suggestion

Remove the openclaw block from the frontmatter and keep the existing standard fields (name, version, description). If categorization or requirements metadata is needed, use flat keys that don't reference an external standard:

---
name: gws-calendar
version: 1.0.0
description: "Google Calendar: Manage calendars and events."
category: productivity
requires:
  bins: ["gws"]
cliHelp: "gws calendar --help"
---