feat: Add practical use case examples and comprehensive gap analysis

- Created invoice template demonstrating business document requirements
- Added design pattern example showing knowledge management use case
- Included sample data file for template + data scenarios
- Comprehensive gap analysis identifying 6 critical tooling limitations
- Documented 3-phase development roadmap for enhanced capabilities
- Based on Issue #63 use case brainstorming requirements

Key gaps identified:
1. Template engine for dynamic document generation
2. Calculation system for mathematical operations
3. Batch processing for multi-document workflows
4. External data integration capabilities
5. Cross-document relationship management
6. Advanced output format support

Ready for requirements engineering and epic decomposition.

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

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

examples/invoice_template.md

@@ -0,0 +1,62 @@
+---
+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}}"
+```