Document Lastenheft processing order

[hindermath]

Summary

• Add Lastenheft_Abarbeitungsreihenfolge.md as the durable processing order for later Spec Kit runs.
• Link the order from README.md and docs/README.md.
• Update docs/project-statistics.md for the documentation change.

Validation

• git diff --check
• Not run: dotnet build/test/docfx, docs-only change.

[Copilot]

Pull request overview

This PR documents a durable, prioritized processing order for existing Lastenheft*.md requirement intakes to guide future Spec-Kit runs, and links that order from the main READMEs while recording the change in the project statistics ledger.

Changes:

• Add Lastenheft_Abarbeitungsreihenfolge.md defining the active order and a “completed/non-operative” classification.
• Link the new processing-order document from README.md and docs/README.md.
• Update docs/project-statistics.md to record the documentation-only change.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
README.md	Adds a bilingual pointer to the new Lastenheft processing-order document within the Spec-Kit workflow section.
Lastenheft_Abarbeitungsreihenfolge.md	New root-level document capturing the prioritized order and maintenance rules for future Spec-Kit runs.
docs/README.md	Adds a dedicated section linking to the processing-order document for documentation readers.
docs/project-statistics.md	Updates “Stand” date and appends a new ledger entry documenting this docs-only update.