Watch-page button now appears reliably after in-site navigation

This update improves the most important reliability case: opening a video via YouTube SPA navigation (for example, from Home or Search) without refreshing the page.

The extension now uses a stronger mount-target strategy for the watch page and keeps retrying until the button is mounted in the preferred watch metadata area.

Search results behavior remains clean and consistent

On /results, the extension keeps a single button per result item in the intended menu area and avoids duplicate overlay buttons on thumbnails.

Better recovery flow for dynamic YouTube layouts

To reduce missed renders on delayed metadata updates, we improved:

• SPA re-initialization timing
• Backfill retries for late DOM changes
• Watch-page observer target selection

Code quality and maintainability improvements

This release also includes internal cleanup to make future fixes safer and easier:

• Centralized selector configuration
• Reduced redundant mount-path logic
• Added re-initialization deduplication for burst SPA events

These changes are focused on real-world reliability while preserving existing behavior for users who already had stable rendering.