[ricklambrechts]

Updates to the documentation, this does not include all the PRS and NVI changes but this is a start with the layout changes.

• Expand PRS and NVI documentation with updated API examples, OPRF flows, FHIR operations, and service-specific OAuth instructions.
• Clarify onboarding with PKIoverheid certificates, organisation registration, and mTLS connection checks.
• Migrate documentation from HTML templates to Markdown with reusable Hugo shortcodes.
• Improve responsive integration navigation with a section sidebar and active-section highlighting.
• Update service metadata and the changelog, and add a link to the latest documentation in the README.