Improve UI robustness and group/selection handling

[offhub]

Multiple fixes and enhancements across the tray, grouping, and selection logic:

• QSbieAPI/SbieIni: preserve and round-trip empty group entries when serializing/deserializing text maps (emit "Group:" lines and parse empty payloads).

• SandMan (tray & box logic):

  • Update tray icon/tooltip while delete-content operations are in progress, and make m_iDeletingContent decremented safely and initialized on state update.
  • Harden OnBoxDblClick/OnBoxMenu/PopUpMenu with null/empty checks to avoid crashes when items or API are missing.
  • Improve tray widget layout: size policies, spacing, elide mode, alignment and minimum width calculation instead of fixed width.
  • Add user-visible placeholder actions/items when no sandboxes match the tray filter.
  • Fix several recursive Depth++ call sites to use Depth + 1 for clarity and correctness.

• SbieView (grouping & selection):

  • Add NormalizeGroups() to sanitize group data (remove duplicates, cycles, invalid refs) and call it on load/save to keep grouping consistent.
  • Implement selection utilities SelectBoxes, SelectNames and RestoreBoxSelectionLater to preserve/restore selection and scroll post-refresh.
  • Make AddNewBox use a longer singleShot delay to avoid races with proxy/layout timers when selecting newly-created boxes.
  • Coalesce rapid MoveItem calls into a batch (m_MoveBatchPending/m_MoveBatchChanged) to avoid repeated clears/refreshes; restore selection after batch completes.
  • Ensure group create/import/rename/delete operations keep reasonable focus: restore box/group selection or root focus as appropriate.
  • Various small fixes: always ensure the empty root group exists, append new groups to root, and avoid invalid model/index operations.

These changes aim to fix crashes, prevent UI races, keep the user's focus after structural changes, and provide clear feedback in the tray when no sandboxes are present.