docs: add comprehensive CMS documentation

Add complete documentation for the Content Management System:

Feature Documentation (docs/features/):
- content-management-system.md - Complete CMS overview
  * Two-tier architecture explanation
  * Database schema and relationships
  * API reference for all endpoints
  * Usage workflows for admin/vendor/customer
  * Best practices and examples

- cms-implementation-guide.md - Step-by-step implementation
  * Activation checklist
  * Code integration instructions
  * Testing procedures
  * Troubleshooting guide

Quick Start Guide (docs/getting-started/):
- cms-quick-start.md - Quick reference
  * Setup commands
  * Access URLs
  * Managing content (API, admin panel, vendor dashboard)
  * Two-tier system explained with examples
  * Common tasks and troubleshooting

Updated Seeder Docs:
- Add CMS to enhanced seeder coverage list
- Add dedicated CMS section with table of pages
- Document integration with db-setup workflow
- Update best practices

MkDocs Configuration:
- Add "Features" section with CMS documentation
- Add CMS Quick Start to "Getting Started"
- Add CDN Fallback Strategy to "Frontend Development"
- Complete navigation structure

All documentation builds cleanly with no warnings.

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

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

mkdocs.yml

@@ -20,6 +20,7 @@ nav:
       - Overview: getting-started/database-setup.md
       - Complete Setup Guide: getting-started/DATABASE_SETUP_GUIDE.md
       - Quick Reference: getting-started/DATABASE_QUICK_REFERENCE.md
+    - CMS Quick Start: getting-started/cms-quick-start.md
     - Configuration: getting-started/configuration.md
 
   # ============================================
@@ -70,6 +71,7 @@ nav:
   # ============================================
   - Frontend Development:
     - Overview: frontend/overview.md
+    - CDN Fallback Strategy: frontend/cdn-fallback-strategy.md
     - Shared Components:
       - UI Components: frontend/shared/ui-components.md
       - UI Components Quick Reference: frontend/shared/ui-components-quick-reference.md
@@ -130,6 +132,14 @@ nav:
     - Environment Variables: deployment/environment.md
     - Stripe Integration: deployment/stripe-integration.md
 
+  # ============================================
+  # FEATURES
+  # ============================================
+  - Features:
+    - Content Management System:
+      - Overview: features/content-management-system.md
+      - Implementation Guide: features/cms-implementation-guide.md
+
   # ============================================
   # USER GUIDES
   # ============================================