[Testing] No unit test for backend/src/seed/data/remittance.ts field shape

[grantfox-oss]

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Why this matters
backend/src/seed/data/remittance.ts hand builds demo remittance rows that are inserted directly into the database. Nothing asserts the fields it produces match the remittanceSchemas.ts shape, so a schema change can silently desync from the seed data.

Acceptance criteria

• Add a test that validates each seed remittance record against backend/src/schemas/remittanceSchemas.ts
• Test fails loudly if a required field is missing or mistyped

Files to touch

• backend/src/seed/data/remittance.ts
• backend/src/schemas/remittanceSchemas.ts

Out of scope
Rewriting the seed data generator.