docs: update company-vendor management documentation

- Document all admin UI pages (list, detail, edit)
- Document transfer ownership modal with user search
- Add user management API endpoints section
- Update ownership transfer description
- Fix encoding issue in marketplace-integration.md

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

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

mkdocs.yml

@@ -30,6 +30,7 @@ nav:
   - Architecture:
     - Overview: architecture/overview.md
     - Architecture Patterns: architecture/architecture-patterns.md
+    - Company-Vendor Management: architecture/company-vendor-management.md
     - Multi-Tenant System: architecture/multi-tenant.md
     - Middleware Stack: architecture/middleware.md
     - Request Flow: architecture/request-flow.md
@@ -82,6 +83,8 @@ nav:
   - Frontend Development:
     - Overview: frontend/overview.md
     - CDN Fallback Strategy: frontend/cdn-fallback-strategy.md
+    - Tailwind CSS Build: frontend/tailwind-css.md
+    - Tailwind v3 Migration Plan: frontend/tailwind-migration-plan.md
     - Shared Components:
       - UI Components: frontend/shared/ui-components.md
       - UI Components Quick Reference: frontend/shared/ui-components-quick-reference.md