Extract search-and-open UI into OpenItemWidget (open_search.py), a
plain QWidget with item_selected/cancelled signals. Silo_Open now
adds this widget as an MDI subwindow instead of running a blocking
QDialog, matching the Silo_New tab pattern.
Improvements over the old dialog:
- Non-blocking: multiple search tabs can be open simultaneously
- 500 ms debounce on search input reduces API load
- Filter checkbox changes trigger immediate re-search
forbes-0023
be8783bf0a