feat(core,app,android,ios): add a first share without a detour or a name to invent

The empty library said to add a link "under Shares, then refresh" with
nothing to press on the phones, and on the desktop only switched page.
All three now open the add form from there, the desktop with the caret
in the link field; and adding already crawls, so there is nothing to
refresh.

A share's name was required before the viewer had seen anything to name.
It is optional now: without one, ShareStore::add_verified takes the
shared folder's own name from the link it has just opened. The link
comes first in each form. The desktop form submits on Enter, and the
Android link field has an eye to check what was pasted.

ios/ProtonStream/UI/LibraryView.swift

@@ -57,6 +57,7 @@ struct LibraryView: View {
     @Environment(\.scheme) private var scheme
     let onResume: (TitleRecord, Int) -> Void
     let onTitle: (TitleRecord) -> Void
+    var onAddShare: () -> Void = {}
 
     // What a long press opened a menu for: a title, or a Continue watching card.
     @State private var menuFor: TitleRecord?
@@ -146,7 +147,11 @@ struct LibraryView: View {
             EmptyState("Nothing matches", "No title in the library is called “\(model.query.trimmingCharacters(in: .whitespaces))”.")
         } else if model.titles.isEmpty {
             ScrollView {
-                EmptyState("Your library is empty", "Add a Proton Drive public link under Shares, then refresh.")
+                EmptyState(
+                    "Your library is empty",
+                    "Add a Proton Drive share link, and everything playable behind it shows up here.",
+                    action: ("Add a share", onAddShare)
+                )
                     .containerRelativeFrame(.vertical)
             }
             .refreshable { await model.crawlNow(nil) }