Implement functional settings page and wire all settings entry points

[Yashb404]

Summary

Settings route exists conceptually but user-visible settings interactions are incomplete or non-functional.

Current Behavior

• Settings button may be present but does not consistently open a usable page.
• Settings controls are missing or not connected to persisted state.

Expected Behavior

• Settings page is fully functional and reachable from all expected entry points.
• Changes persist and are reflected across app surfaces where applicable.

Scope

• Implement or complete settings page UI.
• Wire settings navigation from header/menu/editor contexts.
• Connect settings to backend/local persistence where required.
• Add basic validation and success/error feedback.

Acceptance Criteria

• Settings page opens from all defined entry points.
• At least core settings can be changed and persisted.
• Saved settings are reflected after reload.
• Error states are clear when save fails.