v0.2.0 — Relaunch as Cal + ValueGuard

Relaunch as Cal (askcal.io) + ValueGuard.

• Repointed to the Cal API. DEFAULT_BASE_URL is now https://api.askcal.io;
  the legacy vault.homeloanexpress.ai host is retired. Users who set
  CAL_API_BASE_URL explicitly need no change.
• Rebranded the package to @askcal/mcp-server. Docs, URLs, homepage, and
  the contact address now point at askcal.io. The server-side Origin header
  is the canonical Cal origin.
• New tool cal_valuation (8 tools total): ValueGuard comparable-sales
  valuation. Pass a subject property and 4+ comps, get an indicated market
  value, floor/ceiling range, over/under-priced verdict, confidence, and the
  comps used. Backed by the Cal API valuation_report executor.
• No breaking changes to the seven existing tool schemas.