fix(helpers): resolve domain skills for subdomains and hyphenated hosts

[hnshah]

Summary

goto() extracts domain skills by taking the first segment of the hostname (booking.com → booking). This misses:

• Hyphenated folders: booking.com → folder is booking-com, not booking
• Subdomains: old.reddit.com → looks for old, should find reddit
• Multi-segment hosts: itch.io → folder is itch-io, archive.org → folder is archive-org

Added _skill_dir() which tries a fallback chain:

1. Each hostname segment left-to-right (old.reddit.com → try old, then reddit, then com)
2. Full hostname hyphenated (booking.com → booking-com)

Before / after

URL	Before	After
booking.com	❌ booking (missing)	✅ booking-com
old.reddit.com	❌ old (missing)	✅ reddit
itch.io	❌ itch (missing)	✅ itch-io
archive.org	❌ archive (missing)	✅ archive-org
reddit.com	✅ reddit	✅ reddit (unchanged)
github.com	✅ github	✅ github (unchanged)

Test plan

• Unit-tested _skill_dir() against 11 URLs covering all cases
• Live-tested with goto("https://www.booking.com") — returns domain_skills: ["scraping.md"]
• Live-tested with goto("https://old.reddit.com") — returns domain_skills: ["scraping.md"]
• Existing matches (github.com, reddit.com, stackoverflow.com) still resolve correctly

---

Summary by cubic

Fixes domain-skill resolution in goto() to correctly handle subdomains and hyphenated or multi-segment hosts. Adds _skill_dir() with a fallback search over hostname segments and the hyphenated full host.

• Bug Fixes
  • Subdomains now resolve to the main domain folder (e.g., old.reddit.com → reddit).
  • Hyphenated and multi-segment hosts resolve to the hyphenated folder (e.g., booking.com → booking-com, itch.io → itch-io).
  • Returns domain_skills only when a matching folder exists; otherwise response is unchanged.

^{Written for commit a9299f7. Summary will update on new commits.}

[cubic-dev-ai]

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