Add admin ecash issuance flow for mint quotes

[joelklabo]

Summary

• add a new admin GraphQL mutation mint_nut04_admin_issue that creates a NUT-04 mint quote via mint API and immediately forces the quote to PAID via mint RPC
• add an Issue Ecash (Admin) action in Mint Database UI with a form for amount/unit/method/description
• wire client query/service/types for the new mutation and refresh mint quote data after issuance
• add server unit tests for new mint API quote creation and admin issuance service flow

Why

cashubtc/nutshell#556 calls out admin-level issuance without requiring payment as a remaining requirement for admin UI flows.

Validation

• npx jest src/server/modules/cashu/mintapi/cashumintapi.service.spec.ts src/server/modules/api/mint/mintquote/mintmintquote.service.spec.ts
• npx tsc -p tsconfig.server.json --noEmit
• npx eslint on all touched TS files

Notes

• Full npm run build is currently blocked in this environment because schema/codegen bootstrap is not available (schema.gql generation step exits non-zero).