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/invoice_data.json

@@ -0,0 +1,37 @@
+{
+  "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
+}