[BUG][STELLAR ADDRESSES] Preserve canonical StrKey case and validate wallet fields

[Obiajulu-gif]

Summary

Administrative user routes lowercase wallet values before storing them, while the user schema accepts arbitrary strings. Stellar StrKeys should be decoded and re-encoded canonically rather than treated like case-insensitive emails.

Repository evidence

• app/api/users/route.ts:41-44 lowercases walletAddress; app/api/users/[id]/route.ts:67-70 does the same.
• models/User.ts:89-99 defines unique wallet strings without Stellar validation.

Scope

• Validate account IDs with the shared Stellar StrKey validator and store canonical encoded values.
• Reject contract IDs, muxed accounts, malformed keys, and case-altered values where unsupported.

Acceptance criteria

• Valid G-addresses round-trip unchanged and invalid inputs fail before persistence.
• Existing lowercase/corrupt values receive a safe migration report.

Tests

• Cover canonical, lowercase, wrong checksum, wrong key type, whitespace, and duplicate variants.

Non-goals

• Implementing wallet ownership proof, tracked separately.

[Owolabenjade]

Hello maintainer, I want to work on this issue.

[grantfox-oss]

🦊 GrantFox — @Owolabenjade has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #191)
2. Your PR will be reviewed by the Chainmove maintainers

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