Surface ClawHub skill install

[pdurlej]

Summary

• Add a ClawHub install section and public listing link to README.
• Clarify that the Things Cloud skill works with OpenClaw, Codex, and Claude Code through MCP, with CLI fallback.
• Bump the skill wrapper metadata to 0.1.1 and update publishing docs/changelog.

External Update

• Commented on Add Things Cloud / Things 3 as a Productivity integration openclaw/openclaw#91204 with the live ClawHub listing, CLEAN moderation status, and early 72 install/download signal.

Verification

• Parsed skills/things-cloud/SKILL.md frontmatter with Ruby YAML.safe_load.
• git diff --check
• ASCII scan for touched public docs.
• GOCACHE=/private/tmp/go-build-things go test ./...