Add docs for API error response shape and field guarantees

[Chucks1093]

Summary
The API error response shape is implemented consistently in most places but is not formally documented. Clients and contributors need to know which fields are always present, which are optional, and what values each field can take.

Scope

• document the full error response shape including all possible fields
• note which fields are guaranteed to be present and which are optional
• provide an example error response for each HTTP error category

Acceptance Criteria

• every error response field is documented with its type and presence guarantee
• at least one example is provided for 400, 404, and 500 error categories
• no code changes are required; this is a docs-only issue

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

[Malcolm-Wander]

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

Hello maintainer,I’d love to work on this issue please,I’ve got experience and I promise to work properly,thank you

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Malcolm-Wander to this issue.

[Jonathan-ai9]

@Jonathan-ai9 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi,I’d like to work on this issue. I will document the API error response format, clearly describing field types and guarantees, and provide example responses for 400, 404, and 500 error categories to improve developer experience and client integration.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Jonathan-ai9 to this issue.

[Divineifed1]

@Divineifed1 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hello Maintainer, can I work on this

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[SamixYasuke]

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

Hi maintainer, I’d add a dedicated documentation section that fully defines the API error response structure, clearly listing each field, its type, and whether it is always present or optional. I’d also include concrete example responses for 400, 404, and 500 errors so consumers can reliably integrate without needing to inspect implementation details.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @SamixYasuke to this issue.

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This issue has been completed by @Divineifed1 as part of the Stellar Wave Program's 5th Wave 🥳

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