[P1] Fix broken Settings navigation (404)

[kgarg2468]

Problem

Sidebar includes a /settings route, but no settings page exists, causing a 404.

Scope

• Either implement a basic settings page or remove/disable the Settings nav item until route exists.

Acceptance Criteria

• Clicking Settings does not lead to a 404.
• Navigation only exposes implemented routes.

Suggested Files

• components/layout/Sidebar.tsx
• app/(app)/settings/page.tsx (if creating route)