Reverts commits 47b5e45, 5c76939, 1eecae0, 660208a, 86a9f65, 259d5b6.
Removes PinnedPropertiesBar, usePinnedProperties hook, Rust backend
for _pinned_properties, and all related tests.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>