Implement GET /api/v1/requests with filters and pagination

[iexwr]

Context

src/index.ts only has /requests/:id and /accounts/:address/received. There is no list endpoint, so the dashboard cannot show a user's requests.

Acceptance criteria

• GET /api/v1/requests supports query params: payee, payer (optional), status, asset, limit (default 20, max 100), cursor.
• Returns { data: PaymentRequest[], meta: { total, limit, cursor } }.
• cursor is the id of the last item; subsequent calls pass it to continue.

Technical notes

• Build a Prisma where from present filters; order by id desc.
• Use skip/take for pagination keyed on cursor.
• See src/types.ts for the PaymentRequest shape.

Testing

• Add a vitest route test covering filter + pagination.