Bug: skills new can infer undefined in titles from repeated separators

[ayskobtw-lil]

sh1pt skills new can infer a malformed listing title when the source SKILL.md frontmatter name contains repeated separators.

Repro SKILL.md frontmatter:

---
name: alpha--beta
description: Handles alpha beta workflows.
---

Current behavior:

• name is correctly slugified to alpha-beta
• inferred title becomes Alpha undefined Beta

Expected behavior:

• inferred title should be Alpha Beta
• generated manifests and marketplace commands should not contain the literal word undefined

[ayskobtw-lil]

Fix PR opened: #502

Verification before opening PR:

• npx --yes pnpm@9.12.0 exec vitest run packages/cli/src/commands/skills.test.ts -> 10 passed
• npx --yes pnpm@9.12.0 --filter @profullstack/sh1pt typecheck -> passed