Add frontend-only local decisions template

[Mine77]

Summary

• Adds a reusable front-end-only local decisions template under examples/local-decisions.
• Adds SDK helpers for browser-local decision persistence, update-by-id behavior, and stable JSON export.
• Wires the new example into the root build and documents it in the README.

Closes #12

Screenshots

Desktop:

Mobile:

Tests

• npm test
• npm run check
• npm run lint
• npm run smoke (passes; prints the existing url.parse() deprecation warning before smoke runtime ok)
• Browser QA on http://127.0.0.1:5187/:
  • page loads with 3 seeded local decisions
  • adding a Review speed decision updates the UI to 4 decisions
  • Copy JSON writes all 4 decisions to the clipboard
  • mobile reload still shows the added decision from local storage
  • no console warnings/errors observed