feat(stellar): add passkey signing settings

[charlesejemai-cyber]

Summary

• add a settings page with a passkey opt-in toggle and registration flow
• implement WebAuthn-backed passkey registration/authentication helpers for Stellar signing
• wire Stellar signing to prefer passkeys and fall back to Freighter when unavailable
• document the trust boundary and passkey scope in-app

Verification

• pnpm vitest run src/lib/stellar/passkey.test.ts
• pnpm build

closes #110

[vercel]

@charlesejemai-cyber is attempting to deploy a commit to the truthixify's projects Team on Vercel.

A member of the Team first needs to authorize it.

[drips-wave]

@charlesejemai-cyber 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]

build failing. Most likely prettier drift on SettingsPage.tsx or similar (see the pattern in your sibling PR #130). Run pnpm format and pnpm build locally, commit the fixes.

[Chrisland58]

@truthixify i worked on issue #109
The issue was merged and closed but I got no point awarded to me😭

[truthixify]

CI fails during pnpm setup: onlyBuiltDependencies?.sort is not a function. Please revert or simplify the workflow changes and keep one pnpm setup path matching the repo.