fix: standardize error responses across /v1 routes

[jchinedu]

Closes #266

Description

Linked Issue

Closes #

Type of Change

• 🐛 Bug fix (API or policy engine)
• ✨ New feature / endpoint
• 📝 Documentation / OpenAPI spec update
• 🔧 Chore / refactor / dependency update
• 🧪 Tests only
• ⛓️ Smart contract change (requires extra review)

Changes Made

Test Evidence

npm run test output:

Smart Contract Checklist (complete if ⛓️ checked above)

• All new functions have NatSpec documentation
• All state-changing functions emit events
• forge test passes with no failures
• forge fmt applied
• No deployment to a live network included in this PR

General Checklist

• I have read CONTRIBUTING.md
• This PR is linked to an open issue
• npm run typecheck passes
• npm run lint passes
• npm run test passes — all tests green
• Prisma schema changes include a migration file
• New API endpoints are documented in OpenAPI (via Fastify schema)
• No secrets, keys, or wallet addresses introduced
• .env.example updated if new env variables were added
• Documentation updated if new behaviour was introduced

Screenshots / Recordings

Additional Notes