Preserve SandMan tree expansion choices

Changes #5491

Reworks SandMan tree-state handling so auto-expand acts as the default only for items without a saved preference, while explicit group, sandbox, and process expand/collapse choices keep winning across refreshes and renames. It also makes Find bar Expand All/Collapse All one-shot actions by blocking tree signals, preventing those commands from overwriting the saved state, and keeps the legacy behavior behind `Options/LegacyAutoExpandTree`.