feat(cli,domain): support non-global namespace skill download

[XiaoSeS]

Changes

• CLI: Parse namespace from skill name using -- separator (e.g., astroclaw--api-gateway)
• Backend: Allow anonymous download for any PUBLIC skill regardless of namespace

Why

Users had to use --namespace flag for non-global skills, and anonymous download was artificially restricted to global namespace only despite skills being marked PUBLIC.

Usage

# Install from non-global namespace
skillhub install astroclaw--api-gateway

# Anonymous download a PUBLIC team-namespace skill
curl /api/skills/team-ai/demo-skill/versions/1.0.0/download

--namespace flag still takes precedence when explicitly specified.

Implementation

CLI changes

• New cli/src/shared/skill-name-parser.ts utility
• install and remove commands updated to parse skill name argument
• 10 unit tests covering edge cases

Backend changes

• SkillDownloadService.isAnonymousDownloadAllowed: drop namespace type check, require only PUBLIC visibility
• Removed unused NamespaceType import
• Test updated to expect success for team-namespace public skill

Testing

✅ skillhub-domain compiles cleanly
✅ skill-name-parser test suite: 10/10 passed

Origin

Synced from SAAS commit 26c67e3

Fixes #490

[CLAassistant]

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