[IP-126]: implement peppol

[nielsdrost7]

Given the work already in PR #471, the remaining Sprint 5 deliverables are:

• Make UblHandler::generateXml() produce real UBL 2.1 XML — this unblocks NLCIUS ([Invoices]: NLCIUS (Dutch CIUS) e-invoicing profile for UBL 2.1 export #487), BE, NL, and most of Europe
• Fix recommendedForCountry('NL') → UBL_21 (one line)
• Promote SendInvoiceToPeppolAction to a Filament Action and wire it to EditInvoice
• Add Peppol fields to customer form (conditional on EU country)
• Add LetsPeppolProvider directory + tests
• Add feature test for the end-to-end send flow

Summary by CodeRabbit

Release Notes

New Features

• Peppol E-Invoicing Integration: Send invoices to Peppol networks with support for multiple providers and document formats
• Multi-Format Support: Automatically select appropriate invoice formats based on customer country (UBL, FatturaPA, Factur-X, EHF, OIOUBL, and others)
• Transmission Tracking: Monitor invoice transmission status with automatic polling and retry capabilities for failed transmissions
• Peppol ID Validation: Validate customer Peppol identifiers against the network before sending
• Provider Management: Configure and test Peppol provider integrations with support for e-invoice.be and Storecove

Addresses #126

[nielsdrost7]

@coderabbitai full review

[coderabbitai]

✅ Action performed

Full review finished.

[b12f]

Hey @nielsdrost7 both this and #473 seems like huge PRs do to in 2 commits with apparently little oversight. v1 has some overly generous AI coding as well, but it does not seem to be as bad. This feels like it will turn into a maintenance nightmare.

[nielsdrost7]

@b12f thanks for tagging me.
You're correct about V1 and AI.
I'll definitely keep an eye on that one, but it has a specific reason.

Don't worry about #473 for a while, I had it working some time ago.
Basically those import menu items are in 2 locations and that blows up the PR. Above all it needed methods in the Services and it needed phpunit tests, so it blew up a bit more.

You're correct about this PR, but i'll keep an eye on it.
It's actually the reason why I kept if from the develop branch and I was thinking "too big".
If you want to help with this Peppol thing, just let me know, I could use some help.

I squashed some commits, therefore it looks big, but trust me, I developed it diligently

I can be found on Discord: https://discord.gg/PPzD2hTrXt