refactor: reorganize examples directory with topic-based subdirectories

Reorganize examples directory into logical topic-based subdirectories with
comprehensive documentation:

- templates/: ISO/ARC42 documentation templates
- asset-management/: Asset management prototypes and demos
- essays/: Long-form content examples
- invoicing/: Invoice generation examples
- plugins/: Plugin development examples
- issue-demos/: Issue prevention demonstrations
- design-patterns/: Design pattern examples

Each subdirectory includes a README.txt file with topic description and
contributor signatures based on file creation timestamps.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

examples/invoicing/README.txt

@@ -0,0 +1,11 @@
+Invoicing System Examples
+
+This directory contains examples for invoice generation and template systems:
+
+- invoice_template.md: Markdown template for invoice generation
+- invoice_data.json: Sample invoice data in JSON format for template population
+
+These examples demonstrate how MarkiTect can be used for business document generation
+with data-driven template systems.
+
+--worsch, 25-10-03