[tui] Add bottom status bar with help text.

Fixes #3

src/tui/logger.rs

@@ -33,7 +33,11 @@ impl Logger {
     pub fn new() -> Self {
         Self {
             state: TuiWidgetState::new(),
-            component_state: Default::default(),
+            component_state: ComponentState::default().with_help_text(concat!(
+                "Q: Quit | Tab: Switch state | ↑/↓: Select target | f: Focus target",
+                " | ←/→: Display level | +/-: Filter level | Space: Toggle hidden targets",
+                " | h: Hide target selector | PageUp/Down: Scroll | Esc: Cancel scroll"
+            )),
         }
     }
 }