refactor(api): harden invoice, auth, and escrow services

[Calebux]

Summary

• optimize invoice batch publishing with a set-based lookup and bulk transactional save
• sanitize invoice updates, isolate repository failures, and restore admin invoice rejection support
• keep auth challenge and verification rate-limit budgets independent while preserving 401 behavior for invalid signatures
• validate escrow inputs and add structured RPC errors with configurable timeouts
• repair baseline CI fixtures discovered during full validation

Validation

• npm run lint
• npm run type-check
• npm run build
• npm run test:ci (94 suites passed; 755 tests passed; 2 skipped)

Closes #304
Closes #305
Closes #306
Closes #307

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