Fix generated tour text limits

[HartBrook]

Summary

• align the structured-output schema with the server's text-length validation
• tell all model providers the exact output limits, including the 420-character finding-body cap
• centralize the limits to prevent schema and validation drift
• prepare patch release 0.2.5

Verification

• npm test
• npm run typecheck
• npm run build
• npm run test:e2e
• npm run test:package
• npm pack --dry-run

Risk and privacy

This changes provider output constraints only. It does not expand source handling, persistence, or GitHub write behavior. No UI screenshots are needed.

Checklist

• The change is focused and documented.
• Tests cover behavior changes.
• npm test, npm run typecheck, and npm run build pass.
• Screenshots are not applicable; there is no visible UI change.
• No credentials, private source, or local Wingdiff data are committed.