Email library: reset select-mode + selectedUids on open

Was sticking on toggled-on state if the user closed the library
while in select-mode — reopening showed the Cancel/X toggle even
though no emails were selected. Force-reset state._selectMode and
state._selectedUids in openEmailLibrary so each open starts fresh.

static/js/emailLibrary.js

@@ -788,6 +788,10 @@ export function openEmailLibrary(opts = {}) {
   state._libOffset = 0;
   state._libSearch = '';
   state._libSearchDraft = '';
+  // Reset select-mode on each open so the toolbar Select button
+  // never opens already-toggled-on after a previous session.
+  state._selectMode = false;
+  if (state._selectedUids) state._selectedUids.clear();
   state._libSearchPills = [];
   _libSuggestionCache = null;
   state._libFilter = 'all';