refactor: standardize markdown file naming to kebab-case convention

Renamed all documentation files to follow kebab-case naming standard:
- UPPERCASE files → lowercase (e.g., RBAC.md → rbac.md)
- snake_case files → kebab-case (e.g., icons_guide.md → icons-guide.md)
- SCREAMING_SNAKE_CASE → kebab-case (e.g., DATABASE_SETUP_GUIDE.md → database-setup-guide.md)

Files renamed (15 total):
API Documentation:
  - api/RBAC.md → api/rbac.md

Architecture:
  - architecture/API_CONSOLIDATION_PROPOSAL.md → api-consolidation-proposal.md
  - architecture/API_MIGRATION_STATUS.md → api-migration-status.md

Development:
  - development/AUTH_DEPENDENCIES_GUIDE.md → auth-dependencies-guide.md
  - development/CUSTOMER_AUTHENTICATION_IMPLEMENTATION.md → customer-authentication-implementation.md
  - development/CUSTOMER_AUTH_SUMMARY.md → customer-auth-summary.md
  - development/icons_guide.md → icons-guide.md

Database Seeder:
  - database-seeder/DATABASE_INIT_GUIDE.md → database-init-guide.md
  - database-seeder/DATABASE_QUICK_REFERENCE_GUIDE.md → database-quick-reference-guide.md
  - database-seeder/DATABASE_SEEDER_DOCUMENTATION.md → database-seeder-documentation.md
  - database-seeder/MAKEFILE_DATABASE_SEEDER.md → makefile-database-seeder.md

Error Rendering:
  - error-rendering/ERROR_RENDERING_DEVELOPER_DOCUMENTATION.md → error-rendering-developer-documentation.md
  - error-rendering/HTML_ERROR_RENDERING_FLOW_DIAGRAM.md → html-error-rendering-flow-diagram.md

Getting Started:
  - getting-started/DATABASE_QUICK_REFERENCE.md → database-quick-reference.md
  - getting-started/DATABASE_SETUP_GUIDE.md → database-setup-guide.md

Updates:
- Updated all references in mkdocs.yml
- Updated all cross-references in markdown files
- Verified mkdocs builds without warnings or errors

Standard: Use kebab-case (lowercase-with-hyphens) for all markdown files

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

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

docs/api/authentication.md

@@ -1253,7 +1253,7 @@ For a condensed cheat sheet of authentication patterns, see [Authentication Quic
 
 ## Related Documentation
 
-- [RBAC System](RBAC.md) - Role-based access control and permissions
+- [RBAC System](rbac.md) - Role-based access control and permissions
 - [Architecture Overview](../architecture/auth-rbac.md) - System-wide authentication architecture
 - [Backend Development](../backend/overview.md) - Backend development guide
 - [API Reference](../backend/middleware-reference.md) - Auto-generated API documentation

docs/api/error-handling.md

@@ -287,6 +287,6 @@ async def invalid_token_handler(request, exc):
 ## Related Documentation
 
 - [Authentication](authentication.md) - Authentication-related exceptions
-- [RBAC](RBAC.md) - Authorization and permission exceptions
+- [RBAC](rbac.md) - Authorization and permission exceptions
 - [Rate Limiting](rate-limiting.md) - Rate limit error handling
 - [Testing Guide](../testing/testing-guide.md) - Testing error scenarios

docs/api/shop-api-reference.md

@@ -832,7 +832,7 @@ POST /api/v1/shop/auth/login
 - ✅ Cleaner URLs (~40% shorter)
 - ✅ Same functionality, better architecture
 
-**See:** [API Migration Status](../architecture/API_MIGRATION_STATUS.md)
+**See:** [API Migration Status](../architecture/api-migration-status.md)
 
 ---
 
@@ -908,4 +908,4 @@ For live API testing and exploration:
 
 ---
 
-**Questions?** See the [API Migration Status](../architecture/API_MIGRATION_STATUS.md) or [Shop Architecture Guide](../frontend/shop/architecture.md).
+**Questions?** See the [API Migration Status](../architecture/api-migration-status.md) or [Shop Architecture Guide](../frontend/shop/architecture.md).