feat: fix sidebar capitalization for MAC, RBAC, and API sections (#42)

Author: Copilot

content/docs/api/index.mdx

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+---
+title: API
+description: Casbin API Reference
+---
+
+# API Reference
+
+This section provides comprehensive documentation for Casbin's APIs, including management APIs, RBAC APIs, and more.
+
+## Casbin APIs
+
+Explore the Casbin API documentation:
+
+- [API Overview](./api-overview) - Introduction to Casbin APIs
+- [Management API](./management-api) - Core management functions
+- [RBAC API](./rbac-api) - Role-based access control operations
+- [RBAC with Domains API](./rbac-with-domains-api) - Multi-tenant RBAC operations
+- [RBAC with Conditions API](./rbac-with-conditions-api) - Conditional RBAC operations
+- [Role Manager API](./role-manager-api) - Role management operations

content/docs/model/mac/index.mdx

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+---
+title: MAC
+description: Mandatory Access Control Models
+---
+
+# MAC (Mandatory Access Control)
+
+Mandatory Access Control (MAC) is a security model where access rights are regulated by a central authority based on multiple levels of security. This section covers various MAC models implemented in Casbin.
+
+## MAC Models
+
+Explore the MAC models available in Casbin:
+
+- [MAC Overview](./mac-overview) - Introduction to Mandatory Access Control
+- [BLP (Bell-LaPadula)](./blp) - Confidentiality-focused model
+- [Biba](./biba) - Integrity-focused model
+- [LBAC (Lattice-Based Access Control)](./lbac) - Hierarchical security levels

content/docs/model/rbac/index.mdx

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+---
+title: RBAC
+description: Role-Based Access Control Models
+---
+
+# RBAC (Role-Based Access Control)
+
+Role-Based Access Control (RBAC) is an access control approach that restricts system access to authorized users based on their roles within an organization. This section covers various RBAC models and features in Casbin.
+
+## RBAC Features
+
+Explore RBAC in Casbin:
+
+- [RBAC Overview](./rbac-overview) - Introduction to Role-Based Access Control
+- [Basic RBAC Model](./rbac) - Core RBAC implementation
+- [RBAC with Pattern](./rbac-with-pattern) - Pattern matching in RBAC
+- [RBAC with Domains](./rbac-with-domains) - Multi-tenancy support
+- [RBAC with Conditions](./rbac-with-conditions) - Conditional access control
+- [Casbin RBAC vs. RBAC96](./casbin-rbac-and-rbac96) - Comparison with RBAC96 standard