Add error copy for failed wallet signature request

[Chucks1093]

Summary
When a wallet signature request fails or is rejected by the user, there is no specific error message shown. A targeted error copy for this case helps users understand what happened and what to do next.

Scope

• identify the wallet signature request flow and its failure states
• add specific error copy for a rejected signature and a failed signature
• ensure the copy is distinct from generic wallet connection error messages

Acceptance Criteria

• a rejected signature shows a message specific to that action
• a failed signature shows a message with a suggested next step
• the copy does not appear for unrelated wallet errors

Contributor coordination: if you pick this up, reach out in Telegram for updates or clarification: https://t.me/accesslayerorg

[covenantalade]

@covenantalade has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Let me work on this issue

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[drips-wave]

Congratulations, @covenantalade! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

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