fix: sync skill packs with configured branch

[kriptoburak]

Summary

• Pass the configured skill-pack branch into sync, matching the branch already used by discovery.
• Add a regression test that syncs the TweetClaw pack from its master branch.
• Document TweetClaw as a concrete non-main skill-pack smoke test.
• Refresh TweetClaw setup wording so GitHub and npm are the setup sources, with ClawHub kept as a discovery page while that listing lags behind npm.

Validation

• cd backend && uv sync --extra dev && uv run pytest tests/test_skills_marketplace_api.py -q
• cd backend && uv run black --check app/api/skills_marketplace.py tests/test_skills_marketplace_api.py && uv run isort --check-only app/api/skills_marketplace.py tests/test_skills_marketplace_api.py && uv run flake8 app/api/skills_marketplace.py tests/test_skills_marketplace_api.py
• python3 scripts/check_markdown_links.py
• git diff --check
• Changed-line stale-version, stale-link, dash, and sensitive-value scans
• Link probes: TweetClaw GitHub 200, ClawHub 200, Xquik 200, npm registry @xquik/tweetclaw 1.6.31 with npmSpec @xquik/tweetclaw@1.6.31 and defaultChoice npm; npm web page returned 403 bot protection to automated probe

Outreach Checks

• Searched open and closed issues and PRs for TweetClaw, tweetclaw, @xquik/tweetclaw, Xquik-dev/tweetclaw, ClawHub, Xquik, and x-twitter-scraper before opening this PR.
• No existing TweetClaw placement, PR, or issue was found in this repository before this PR.
• No badge was added because the existing README badges describe Mission Control itself, not an optional example skill pack.

Risk

Low. The runtime change only passes an existing stored field into the existing collection helper, and the added docs describe a manual smoke test.

[Copilot]

Pull request overview

Passes the configured branch from a stored SkillPack into _collect_pack_skills during sync so non-main packs (e.g. TweetClaw on master) clone the correct branch, matching the branch used elsewhere by discovery. Adds a regression test and documents TweetClaw as a concrete non-main smoke test.

Changes:

• sync_skill_pack now forwards pack.branch to _collect_pack_skills.
• New test verifies the configured branch is propagated and the resulting skill is stored.
• README and baseline-config docs describe TweetClaw as a non-main skill-pack example.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
backend/app/api/skills_marketplace.py	Pass pack.branch into _collect_pack_skills during sync.
backend/tests/test_skills_marketplace_api.py	Add regression test for branch propagation; update existing fake signature to keyword-only with branch.
docs/openclaw_baseline_config.md	Add TweetClaw smoke-test walkthrough with canonical links.
README.md	Mention TweetClaw skill pack and document the non-main branch smoke test.