Import custom skills from GitHub URLs

[rogerchappel]

What

Add GitHub URL import support for custom skills, including folder imports with SKILL.md and optional skill.json metadata.

Why

Paperhug should be usable as an external installable skill without shipping Paperhug-specific code inside CrewCMD. A user can paste a GitHub skill folder URL, keep env vars in CrewCMD's vault, assign the imported skill to an OpenClaw-backed agent, and let the runtime execute the installed CLI locally.

How

• /api/skills/import now supports provider: "github" with sourceUrl or url pointing at a GitHub tree/blob/raw skill path.
• The importer fetches SKILL.md, strips frontmatter before storing content, reads optional skill.json or metadata.json, and stores source metadata/config schema on the normal skill row.
• The Skills page custom form can import from a GitHub URL, shows a GitHub source badge, and allows workspace-scoped custom skills rather than requiring companyId.
• Added route tests for successful GitHub folder import and rejection of non-GitHub URLs.

Checklist

• pnpm typecheck passes
• pnpm test passes
• pnpm build passes
• Updated README/docs if needed
• Migration included (if schema changed)
• Screenshots attached (if UI changed)

Notes:

Exact targeted test command: pnpm test -- src/app/api/skills/import/route.test.ts src/lib/skill-config-form.test.ts.

pnpm lint:check passes with existing warnings. pnpm build passes with the existing Turbopack NFT warning from next.config.ts / src/lib/openclaw-config-parser.ts / src/app/api/runtimes/probe/route.ts.