Docs: Architecture — add architecture decision records (ADRs)

[Hexstar-labs]

Description:
There is no documentation of why key technical decisions were made.

Tasks:

• Create docs/adr/ directory
• Write ADR-001: Why Stellar/Soroban over Ethereum
• Write ADR-002: Why NestJS over Express
• Write ADR-003: Why Next.js App Router
• Write ADR-004: Why Soroban persistent storage for credentials
• Use the MADR template format

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[Dydex]

@Dydex has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi boss, I can work on this

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[Nonso-Eze]

@Nonso-Eze has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Can I work on this

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[drips-wave]

Congratulations, @Nonso-Eze! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

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[drips-wave]

This issue has been completed by @Nonso-Eze as part of the Stellar Wave Program's 3rd Wave 🥳

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