fix: add keyboard controls for header (#205)

* fix: add keyboard controls for header/tree

- Allow to use keyboard for header buttons
- Allow to use arrows to open subtrees in the left panel

* Revert left/right arrows control in tree view

Using them prevents scrolling the window left/right

* Follow codestyle, remove unnecessary code

Author: dkobylianskii

src/uproot_browser/tui/header.py

@@ -14,14 +14,14 @@
 
 
 class HeaderCloseIcon(textual.widgets.Button):
-    def on_click(self) -> None:
+    def on_button_pressed(self, _: textual.widgets.Button.Pressed) -> None:
         self.app.exit()
 
 
 class HeaderHelpIcon(textual.widgets.Button):
     app: Browser
 
-    def on_click(self) -> None:
+    def on_button_pressed(self, _: textual.widgets.Button.Pressed) -> None:
         self.app.action_help()