Fix/issue 3926 video player refactor

[pradeep0153]

Closes #3926.

Description

This PR resolves a massive technical debt issue by consolidating our highly complex, duplicated video streaming logic into a single, robust, and highly maintainable React component.

Changes Made

• Conducted a codebase audit and discovered that the exact same 300+ lines of code responsible for initializing the video player (Video.js/Shaka Player), establishing HLS stream connections, and negotiating DRM (Widevine/PlayReady) tokens were copy-pasted across three separate areas: the main CourseView, the marketing PreviewModal, and the AssignmentVideo wrapper.
• Extracted and abstracted this massive block of imperative logic into a clean, declarative <LearnovaPlayer /> component.
• The new component exposes a simplified props interface (e.g., <LearnovaPlayer videoUrl={url} drmConfig={config} onCompletion={handleEnd} />), completely hiding the internal setup complexity from the parent consumers.
• Refactored all three feature areas to consume this new unified component.

Impact

• Maintainability & Bug Reduction: Copy-pasting complex configuration code is a recipe for disaster. Previously, if we needed to update a DRM token header or patch a specific browser's playback bug, developers had to manually track down and update three separate files, inevitably leading to regressions when one was forgotten. By centralizing the video player into a single source of truth, we ensure uniform playback behavior, synchronized analytics tracking, and drastically reduce the surface area for future bugs.