docs(#94): sync PLAN.md, TODO.md, and test expectations with current implementation

Update PLAN.md to reflect full completion of Hippocampus (100%),
Cortex (100%), and all documentation sections. Update TODO.md
checkboxes for all completed P1/P2/P3 items. Fix HierarchyBuilder
test to expect volumes/shelves from ingestText.

Closes #94

Co-authored-by: devlux76 <86517969+devlux76@users.noreply.github.com>

Author: Copilot