docs: clarify ClawHub search source

[kriptoburak]

Summary

Clarifies the ClawHub search-source name and aligns the detailed source-reference order with the 9-source table. This also fixes README setup anchors that fail local Markdown link checks.

Changes

• Rename current ClawSkillHub and ClawhHub references to ClawHub
• Move Anthropic Skills before ClawHub in the detailed source reference so source numbers match README and SKILL.md
• Add ClawHub query guidance for exact package names plus broader OpenClaw plugin or agent-tool task terms
• Fix API key setup anchors in README

Testing

• Tested /fetch-skill <query> with all 9 sources - not run; docs-only source mapping change
• ShellCheck passes on all .sh files
• SKILL.md frontmatter is valid
• CHANGELOG.md updated
• npx --yes markdown-link-check README.md CHANGELOG.md skills/skill-fetch/SKILL.md skills/skill-fetch/references/search-sources.md --quiet
• bash -n install.sh
• python3 -c "import py_compile; py_compile.compile('install.py', doraise=True)"
• git diff --check

Checklist

• My code follows the project's style guidelines
• I have updated the documentation accordingly
• I have added/updated the CHANGELOG entry