FIX validate invoices before AEAT submission

[braito4]

Summary

Strengthens local invoice validation before generating or sending an AEAT payload.

Checks include:

• complete and non-empty invoice identification
• supported invoice type
• issuer and description length limits
• recipient requirements, including forbidding recipients on F2/R5
• recipient and breakdown count limits
• mandatory chain configuration
• SHA-256 fingerprint format

Validation

Focused valid and invalid invoice cases pass on PHP 8.3, 8.4 and 8.5; syntax and git diff --check pass.