Add describe() method to WraithError subclasses (#173)

[Jerryvic911]

Closes #173

Summary

Adds an optional describe(): string method to the WraithError base
class with a generic fallback, overridden on all concrete subclasses
with a hint templated from this.context. Each hint includes 1-2
concrete next steps plus the docs anchor, so console output and error
toasts can surface useful guidance without a docs round-trip.

Changes

• src/errors.ts: base describe() fallback + tailored overrides on
  every concrete subclass
• test/errors.test.ts: test.each-based suite asserting describe()
  returns a non-empty, tailored hint (not the generic fallback) for
  every subclass
• docs/errors.md: new "Actionable Fix Hints with describe()"
  section with a worked example

Notes

• The issue mentions 18 concrete error classes; I only found 16 in
  src/errors.ts on develop. Happy to add more if any are missing
  elsewhere — let me know if I'm missing something.
• No changes to .message or .toJSON() output — verified via the
  existing instanceof/JSON tests, which all still pass unmodified.
• src/chains/stellar/errors.ts (Soroban contract error decoding) is
  a separate, unrelated system and wasn't touched.

Testing

pnpm exec vitest run test/errors.test.ts — 33/33 passing (17
existing + 16 new).

[drips-wave]

@Jerryvic911 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[truthixify]

Thanks @Jerryvic911. Same story as the run above: test (20) and test (22) fail on pnpm api:check, not on a test. Adding describe() to the error classes changes the public surface, so etc/sdk.api.md needs regenerating:

pnpm build
git add etc/
git commit -m "chore: refresh api-extractor baseline"
git push

The error work itself looks fine, all other jobs are green.

[truthixify]

Merged. Quick turnaround on the baseline @Jerryvic911, and a hint per error subclass rather than one generic string is what makes this actually useful in a console.