list skills: filter by olostep prefix

[ZeeshanAdilButt]

Summary

olostep list skills was iterating every entry in the shared lockfile at ~/.agents/.skill-lock.json. Because that file is shared with any other CLI that follows the agent-skills convention, leftover entries from previously-installed tools (e.g. an old install of another scraping CLI) leaked into our output — showing 42 "skills" instead of the 13 we actually manage.

Fix: skip lockfile entries whose folder name doesn't start with olostep- in listInstalledSkills. The remove path already had this check; iterSkillEntries (used by removeAll) was already safe.

Before

Olostep skills installed (42)
  ✗ firecrawl-build-scrape
  ✗ firecrawl-crawl
  ... (29 foreign rows)
  ✓ scrape
  ...

After

Olostep skills installed (13)
  ✓ scrape
  ✓ map
  ... (13 olostep rows)

Test plan

• 4 new tests in src/lib/skills.test.ts covering: mixed lockfile, all-foreign lockfile, missing lockfile, olostep entry with missing canonical path
• 75/75 unit tests pass
• Manual: olostep list skills on a machine with 29 foreign entries returns only 13 olostep ones