docs: add marketing documentation with outreach templates and pricing

Add comprehensive marketing folder with vendor outreach strategy:
- Feature list and roadmap with status indicators
- Pricing tiers (Starter EUR 49, Professional EUR 99, Business EUR 199)
- Letzshop automation outreach templates (email, phone, LinkedIn)
- Website vendor strategy (connector vs migration options)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

mkdocs.yml

@@ -215,6 +215,17 @@ nav:
   - Troubleshooting:
     - Shop Frontend: troubleshooting/shop-frontend.md
 
+  # ============================================
+  # MARKETING (Business Development)
+  # ============================================
+  - Marketing:
+    - Overview: marketing/index.md
+    - Feature List & Roadmap: marketing/features.md
+    - Pricing Strategy: marketing/pricing.md
+    - Outreach Templates:
+      - Letzshop Automation: marketing/outreach/letzshop-automation.md
+      - Website Vendors: marketing/outreach/website-vendors.md
+
 # Theme configuration
 theme:
   name: material