Continue Phase 18 mechanical migration of centered dialogs to the
shared terminal::popup::render_popup() shell (MC-matching rounded
borders + drop shadow):
permission, owner, connection_dialog, config_dialog,
compare, sort_dialog, progress
All 7 share the same pattern: inline Clear + Block + title replaced
with render_popup() + centered_cols_rect()/centered_percent_rect().
Title color now derives from [dialog] dtitle via the unified shell.
compare.rs also dropped its local centered_rect helper (used only
for the popup shell; the body Block stays inline since it's a
sub-frame, not the popup shell).
Tree (full-screen directory tree dialog) intentionally skipped — it
uses the entire frame area, not a centered popup, so it does not
benefit from the popup shell or shadow.
Tests: 1112 passed (no regressions).
vasilito
2b2b5803ba