Fix#7364 file explorer refresh collapsing tree and add scoped folder refresh

[leehaut]

Fix #7364

Improves the Hop GUI file explorer refresh behaviour so that refreshing no longer collapses the entire tree, and fixes several related edge cases around deletion and project switching.

• Scoped refresh: When the user has selected a folder (or a file inside a folder), F5 / the refresh toolbar action refreshes only that folder via refreshFolder(), preserving expanded state elsewhere in the tree. If nothing has been selected, behaviour falls back to a full tree rebuild.
• Smarter expand-state restore: Replaces TreeMemory.setExpandedFromMemory() with restoreTreeItemExpandedFromMemory(), which loads lazy-loaded folders before expanding them. This prevents blank placeholder rows after refresh.
• Delete handling: After deleting a file or folder, the parent folder is refreshed in place, lastSelectedFolderPath is updated to the parent, and stale tree nodes are removed.
• Project switching: When the explorer root changes (e.g. switching projects), lastSelectedFolderPath and per-tree TreeMemory state are cleared, and scoped refresh is only allowed for paths under the current project root.