Implement URL-based folder routing for intuitive browser back button navigation

[DreamBot706]

Problem Description

Currently, folder navigation inside a course is managed purely via in-memory Redux state while keeping the browser URL fixed at /browse/:code. As a result:

1. Browser Back Button Misbehavior: Pressing the browser's back button (or mouse/mobile back gesture) navigates away from the course page entirely (e.g., back to Dashboard) instead of stepping out of the current subfolder.
2. Lack of Deep Linking: Users cannot bookmark or share direct URLs to specific folders within a course.
3. Loss of Context on Refresh: Reloading the page (F5) resets folder navigation back to the top-level course root.

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Proposed UX Enhancement

Enable individual URL routes for subfolders (e.g., /browse/:code/:folderId) so that folder navigation updates browser history natively.

Key Goals

• Native browser back and forward button support for stepping through subfolders.
• Shareable and bookmarkable direct links to specific subfolders.
• Page refresh resilience preserving the current folder location.