feat: add ClawHub publishing workflow

[ningzimu]

Summary

• Add a GitHub Actions workflow to publish the codex-ppt skill to ClawHub with CLAWHUB_TOKEN.
• Support manual workflow dispatch and v* tag publishing, including automatic SKILL.md version synchronization before upload.
• Add ClawHub/OpenClaw skill metadata and a .clawhubignore file to keep local runtime artifacts out of releases.
• Remove the unused --api-key-stdin runtime option after ClawHub's scanner flagged the stdin variable as suspicious in a manual 0.1.0 publish test.

Manual ClawHub test

• Published codex-ppt@0.1.0 manually with clawhub 0.12.3.
• Found relative publish paths fail locally with "Path must be a folder"; the workflow now publishes via an absolute skill path.
• Verified uploaded files excluded .venv, pycache, and .DS_Store.

Validation

• ruby -e "require 'yaml'; YAML.load_file('.github/workflows/publish-clawhub-skill.yml'); puts 'workflow yaml ok'"
• python3 -m py_compile skills/codex-ppt/scripts/codex_ppt_runtime.py skills/codex-ppt/scripts/image_gen.py skills/codex-ppt/scripts/assemble_ppt.py skills/codex-ppt/scripts/remove_chroma_key.py
• git diff --check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Remove optional .env from required config metadata

Declaring ~/.codex-ppt-skill/.env under metadata.openclaw.requires.config marks that file as a hard runtime requirement, but this skill is designed to work without local API fallback config (built-in image generation path, and OPENAI_API_KEY is explicitly optional in envVars). In OpenClaw/ClawHub requirement checks, this can surface as an unmet prerequisite for fresh installs and block or warn users before they can use the skill in no-API scenarios; this should be moved to optional metadata or omitted from requires.

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