docs: update 2-7-e-invoicing-peppol.md

[habib424]

Drafted by Ship Ship 🚢 — confidence 🟡 medium

What changed

Added VeriFactu network support for Spanish e-invoicing tax reporting. Documented VeriFactu's network overview (Spain-specific tax reporting, no inbox required), registration flow via hosted wizard, and noted that unlike Peppol/myDATA, VeriFactu registration doesn't require entering an e-invoice address in entity settings.

Source PRs

• light#7223 — feat(einvoicing): VeriFactu network + Invopop supplier onboarding

How to use this PR

1. Review the diff against the existing article — focus on accuracy and customer voice.
2. Merge if it reads well. Edit and push to this branch if it needs adjustment.
3. Close without merging if the article doesn't actually need this update.

Once we have a track record of clean drafts, we'll graduate to auto-merge with a delay buffer. For now: human-in-the-loop.