Add 'Create Folder' to folder picker dialog

Adds an input field and button to create a new folder inside the
currently selected directory, then refreshes the tree.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tui/gniza.tcss

@@ -154,6 +154,21 @@ Select {
     height: 1fr;
 }
 
+#fp-new-row {
+    height: auto;
+    margin: 1 0 0 0;
+}
+
+#fp-new-row Input {
+    width: 1fr;
+}
+
+#fp-new-row Button {
+    width: auto;
+    min-width: 16;
+    margin: 0 0 0 1;
+}
+
 #fp-buttons {
     height: auto;
     margin: 1 0 0 0;

tui/widgets/folder_picker.py

@@ -1,8 +1,9 @@
+from pathlib import Path
+
 from textual.app import ComposeResult
 from textual.screen import ModalScreen
-from textual.widgets import DirectoryTree, Header, Footer, Static, Button
+from textual.widgets import DirectoryTree, Static, Button, Input
 from textual.containers import Horizontal, Vertical
-from pathlib import Path
 
 
 class _DirOnly(DirectoryTree):
@@ -23,20 +24,49 @@ class FolderPicker(ModalScreen[str | None]):
         with Vertical(id="folder-picker"):
             yield Static(self._title, id="fp-title")
             yield _DirOnly(self._start, id="fp-tree")
+            with Horizontal(id="fp-new-row"):
+                yield Input(placeholder="New folder name", id="fp-new-name")
+                yield Button("Create Folder", id="fp-create")
             with Horizontal(id="fp-buttons"):
                 yield Button("Select", variant="primary", id="fp-select")
                 yield Button("Cancel", variant="default", id="fp-cancel")
 
+    def _get_selected_path(self) -> Path | None:
+        tree = self.query_one("#fp-tree", DirectoryTree)
+        node = tree.cursor_node
+        if node and node.data and node.data.path:
+            return node.data.path
+        return None
+
     def on_button_pressed(self, event: Button.Pressed) -> None:
         if event.button.id == "fp-select":
-            tree = self.query_one("#fp-tree", DirectoryTree)
-            node = tree.cursor_node
-            if node and node.data and node.data.path:
-                self.dismiss(str(node.data.path))
-            else:
-                self.dismiss(None)
+            path = self._get_selected_path()
+            self.dismiss(str(path) if path else None)
+        elif event.button.id == "fp-create":
+            self._create_folder()
         else:
             self.dismiss(None)
 
+    def _create_folder(self) -> None:
+        name = self.query_one("#fp-new-name", Input).value.strip()
+        if not name:
+            self.notify("Enter a folder name", severity="error")
+            return
+        if "/" in name or "\0" in name:
+            self.notify("Invalid folder name", severity="error")
+            return
+        parent = self._get_selected_path()
+        if not parent:
+            parent = Path(self._start)
+        new_dir = parent / name
+        try:
+            new_dir.mkdir(parents=True, exist_ok=True)
+            self.notify(f"Created: {new_dir}")
+            tree = self.query_one("#fp-tree", DirectoryTree)
+            tree.reload()
+            self.query_one("#fp-new-name", Input).value = ""
+        except OSError as e:
+            self.notify(f"Failed: {e}", severity="error")
+
     def action_cancel(self) -> None:
         self.dismiss(None)