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

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+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

examples/invoicing/invoice_data.json

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+{
+  "invoice_number": "INV-2025-001",
+  "date": "2025-10-02",
+  "due_date": "2025-11-01",
+  "currency": "EUR",
+  "tax_rate": 0.19,
+  "tax_rate_percent": "19",
+  "customer": {
+    "company": "Acme Corporation",
+    "contact": "John Smith",
+    "address": "123 Business Ave, 54321 Commerce City",
+    "email": "john.smith@acme.example"
+  },
+  "line_items": [
+    {
+      "description": "MarkiTect Pro License (1 year)",
+      "quantity": 5,
+      "unit_price": 299.00,
+      "total": 1495.00
+    },
+    {
+      "description": "Implementation & Training",
+      "quantity": 40,
+      "unit_price": 150.00,
+      "total": 6000.00
+    },
+    {
+      "description": "Priority Support Package",
+      "quantity": 1,
+      "unit_price": 500.00,
+      "total": 500.00
+    }
+  ],
+  "subtotal": 7995.00,
+  "tax_amount": 1519.05,
+  "total": 9514.05
+}

examples/invoicing/invoice_template.md

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+---
+document_type: "invoice"
+invoice_number: "INV-2025-001"
+date: "2025-10-02"
+due_date: "2025-11-01"
+currency: "EUR"
+tax_rate: 0.19
+status: "draft"
+---
+
+# Invoice {{invoice_number}}
+
+**Date:** {{date}}
+**Due Date:** {{due_date}}
+
+## Bill To
+Company: {{customer.company}}
+Contact: {{customer.contact}}
+Address: {{customer.address}}
+Email: {{customer.email}}
+
+## Bill From
+Company: MarkiTect Solutions GmbH
+Address: Innovation Street 42, 12345 Tech City
+Email: billing@markitect.example
+Tax ID: DE123456789
+
+## Line Items
+
+| Description | Quantity | Unit Price | Total |
+|-------------|----------|------------|--------|
+{{#each line_items}}
+| {{description}} | {{quantity}} | {{unit_price}} {{../currency}} | {{multiply quantity unit_price}} {{../currency}} |
+{{/each}}
+
+## Summary
+
+**Subtotal:** {{subtotal}} {{currency}}
+**Tax ({{tax_rate_percent}}%):** {{tax_amount}} {{currency}}
+**Total:** {{total}} {{currency}}
+
+---
+
+```yaml tailmatter
+qa_checklist:
+  - requirement: "All line items verified"
+    complete: false
+  - requirement: "Customer details confirmed"
+    complete: false
+  - requirement: "Tax calculation verified"
+    complete: false
+
+editorial:
+  status: "draft"
+  reviewer: "finance.team@markitect.example"
+  approval_required: true
+
+calculations:
+  subtotal: "{{sum line_items 'total'}}"
+  tax_amount: "{{multiply subtotal tax_rate}}"
+  total: "{{add subtotal tax_amount}}"
+```