Add Back and Next Navigation Buttons to Roadmap Learning Panel

Feature Description

In the roadmap.sh learning/resource panel, the navigation currently provides only Done and Skip actions. Add Back and Next buttons so users can move sequentially between roadmap topics without closing the learning panel or returning to the roadmap manually.

Expected Behavior

• Back: Opens the previous roadmap topic/resource.
• Next: Opens the next roadmap topic/resource.
• Keep the existing Done and Skip buttons.
• Navigation should preserve the user's current progress/state.
• Disable or hide Back when the user is on the first topic.
• Disable or hide Next when the user is on the last topic.
• The navigation should work consistently across all roadmap learning panels.