Create access control components (ProtectedRoute, ConditionalRender, FeatureGate) #25

📋 Description

Implement reusable UI and routing guards to enforce access rules and graceful fallback behavior.

✅ Acceptance Criteria

• ProtectedRoute blocks unauthorized navigation and redirects correctly.
• ConditionalRender supports simple permission-based UI display logic.
• FeatureGate enforces granular feature-level access (plan/permission required).
• Unauthorized access states support fallback UI or upgrade CTA patterns.

🔗 Prerequisite Issues

## DoD

• All protected areas use shared guard components.
• Redirect logic handles unauthenticated and unauthorized users distinctly.
• No direct ad-hoc permission checks in critical routes.
• Example usage patterns are documented for contributors.