gui: replace backend/model ComboBoxes with TextField + picker dialogs

- Backend: TextField with '...' button opens ListView of available backends
- Model: TextField with '...' button opens ListView filtered by selected backend
- Auto-populate model placeholder when backend text changes
- Model picker also works on manual click for re-selection
- Update onAccepted to use field.text instead of combo.currentText

gui/main.qml

@@ -303,7 +303,11 @@ ApplicationWindow {
                 }
                 Button {
                     text: "Browse..."
-                    onClicked: folderDialog.open()
+                    onClicked: {
+                        var folder = theme.chooseFolder("Select Project Directory", dirField.text || "")
+                        if (folder !== "")
+                            dirField.text = folder
+                    }
                 }
             }
 
@@ -322,12 +326,14 @@ ApplicationWindow {
             RowLayout {
                 Layout.fillWidth: true
                 Label { text: "Backend:"; Layout.preferredWidth: 80 }
-                ComboBox {
-                    id: backendCombo
+                TextField {
+                    id: backendField
                     Layout.fillWidth: true
-                    enabled: ollie.rootBackendsLoaded
-                    model: ollie.availableBackends
-                    currentIndex: 0
+                    placeholderText: "ollama"
+                }
+                Button {
+                    text: "..."
+                    onClicked: backendPicker.open()
                 }
             }
 
@@ -335,12 +341,16 @@ ApplicationWindow {
             RowLayout {
                 Layout.fillWidth: true
                 Label { text: "Model:"; Layout.preferredWidth: 80 }
-                ComboBox {
-                    id: modelCombo
+                TextField {
+                    id: modelField
                     Layout.fillWidth: true
-                    enabled: ollie.rootModelsLoaded && backendCombo.count > 0
-                    model: ollie.getAvailableModels(backendCombo.currentText)
-                    currentIndex: 0
+                    placeholderText: "(auto-populated)"
+                    enabled: backendField.text.trim() !== ""
+                }
+                Button {
+                    text: "..."
+                    enabled: backendField.text.trim() !== "" && ollie.rootModelsLoaded
+                    onClicked: modelPicker.open()
                 }
             }
 
@@ -368,10 +378,73 @@ ApplicationWindow {
                 }
             }
 
+            // Backend picker dialog
+            Dialog {
+                id: backendPicker
+                title: "Select Backend"
+                anchors.centerIn: parent
+                modal: true
+                standardButtons: Dialog.Cancel
+
+                contentItem: ListView {
+                    width: 300
+                    height: 200
+                    model: ollie.availableBackends
+                    delegate: ItemDelegate {
+                        width: parent.width
+                        text: modelData
+                        onClicked: {
+                            backendField.text = modelData
+                            backendPicker.close()
+                        }
+                    }
+                }
+            }
+
+            // Model picker dialog
+            Dialog {
+                id: modelPicker
+                title: "Select Model"
+                anchors.centerIn: parent
+                modal: true
+                standardButtons: Dialog.Cancel
+
+                contentItem: ListView {
+                    width: 400
+                    height: 300
+                    model: ollie.getAvailableModels(backendField.text.trim())
+                    delegate: ItemDelegate {
+                        width: parent.width
+                        text: modelData
+                        onClicked: {
+                            modelField.text = modelData
+                            modelPicker.close()
+                        }
+                    }
+                }
+            }
+
             Component.onCompleted: {
                 if (!ollie.rootBackendsLoaded) ollie.loadRootBackends()
                 if (!ollie.rootAgentsLoaded) ollie.loadRootAgents()
             }
+
+            Connections {
+                target: backendField
+                function onTextChanged() {
+                    var be = backendField.text.trim()
+                    if (be !== "" && ollie.rootModelsLoaded) {
+                        var models = ollie.getAvailableModels(be)
+                        if (models.length > 0) {
+                            modelField.placeholderText = models[0]
+                        } else {
+                            modelField.placeholderText = "(no models)"
+                        }
+                    } else {
+                        modelField.placeholderText = "(auto-populated)"
+                    }
+                }
+            }
         }
 
         onAccepted: {
@@ -381,8 +454,8 @@ ApplicationWindow {
                 return
             }
             var name = nameField.text.trim()
-            var backend = backendCombo.currentText
-            var model = modelCombo.currentText
+            var backend = backendField.text.trim()
+            var model = modelField.text.trim()
             var agent = agentCombo.currentText
             var remote = remoteField.text.trim()
 
@@ -395,16 +468,6 @@ ApplicationWindow {
         }
     }
 
-    FileDialog {
-        id: folderDialog
-        title: "Select Project Directory"
-        currentFolder: StandardPaths.homePath
-        selectFolder: true
-        onAccepted: {
-            dirField.text = selectedFolder
-        }
-    }
-
     SplitView {
         anchors.fill: parent