feat(qt): search boxes clear on Escape, drop focus, and offer a clear cross

Every search field follows one contract: Escape empties the text AND hands
the keyboard back to the shell root, and a clickable cross clears the text
while keeping the caret in the field. The header search shows the cross
left of the Enter glyph while the cortinilla is open; QbzLineEdit's search
mode and the new QbzSearchField (the album track filter and the playlist
filter) float it at the right edge.

Each field also keeps its focus after an edit unless another text input
took it, and logs when it had to reclaim it.

cc

crates/qbz-qt/qml/shell/HeaderBar.qml

@@ -942,6 +942,24 @@ Rectangle {
     function focusSearch() {
         searchInput.forceActiveFocus()
     }
+    // FOCUS RETENTION (2026-09-13, every search box): after an edit, once the
+    // event loop settles, reclaim the keyboard unless another text input took
+    // it — the dropdown opening or closing must never steal it mid-word.
+    property bool _searchReclaim: false
+    function _reclaimSearchFocus() {
+        if (!root._searchReclaim)
+            return
+        root._searchReclaim = false
+        if (searchInput.activeFocus)
+            return
+        var win = root.Window.window
+        var current = win ? win.activeFocusItem : null
+        if (current instanceof TextInput || current instanceof TextEdit)
+            return
+        console.log("[HeaderBar] search lost focus after an edit; reclaimed (holder was "
+                    + (current ? current.toString() : "none") + ")")
+        searchInput.forceActiveFocus()
+    }
 
     Rectangle {
         id: searchBox
@@ -1001,7 +1019,11 @@ Rectangle {
                     QbzSearch.searchLive(text)
                 }
             }
-            onTextEdited: applyLiveQuery()
+            onTextEdited: {
+                applyLiveQuery()
+                root._searchReclaim = true
+                Qt.callLater(root._reclaimSearchFocus)
+            }
 
             // The Enter rule (HeaderBar.slint on-enter): cortinilla open +
             // a keyboard selection -> activate the row; open + none -> full
@@ -1045,8 +1067,9 @@ Rectangle {
                     // the modals use, not merely cleared: a null
                     // activeFocusItem passes the gate but leaves AppShell's
                     // Keys handler receiving nothing at all.
-                    if (QbzSearch.cortinillaOpen)
-                        QbzSearch.cortinillaDismiss()
+                    // …and it empties the box too (2026-09-13, every search
+                    // box): clearSearch() drops the text and the dropdown.
+                    root.clearSearch()
                     event.accepted = true
                     var p = searchInput
                     while (p.parent) {
@@ -1078,6 +1101,7 @@ Rectangle {
         // open (Slint: it lives in the box, opposite the magnifier), else
         // the × clear.
         Text {
+            id: enterHint
             visible: QbzSearch.cortinillaOpen
             anchors.right: parent.right
             anchors.rightMargin: 10
@@ -1087,10 +1111,13 @@ Rectangle {
             font.pixelSize: 12
             verticalAlignment: Text.AlignVCenter
         }
+        // The clear cross: always there while there is text (2026-09-13); it
+        // sits to the LEFT of the ↵ hint while the dropdown is open, at the
+        // right edge otherwise.
         Rectangle {
-            visible: !QbzSearch.cortinillaOpen && searchInput.text !== ""
-            anchors.right: parent.right
-            anchors.rightMargin: 5
+            visible: searchInput.text !== ""
+            anchors.right: QbzSearch.cortinillaOpen ? enterHint.left : parent.right
+            anchors.rightMargin: QbzSearch.cortinillaOpen ? 4 : 5
             width: 22
             height: 22
             anchors.verticalCenter: parent.verticalCenter