Add expand all/collapse all to the course tree
An "Expand all" link above the tree (toggling to "Collapse all" once everything's open) opens or closes every section at once - on both the lesson page's sidebar and the dashboard's loaded-course view. Toggles stay right-aligned per section, matching convention rather than moving to the left. Label reflects current state on load and persists through the same remembered-sections mechanism as manual expand/collapse. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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