Add named keyboard binding modes (#32)

Add named keyboard shortcut maps with an Escape exit and a panel indicator. Keep press/release ownership across transitions, validate remapped Escape keys, and cancel stale repeats and focus previews.

Give the indicator ownership of the panel while a mode is active. Close popovers, collapse Morph, and keep Live Activities data current without resizing the hidden panel. Document configuration and transition behavior.

Validation: 1,519 workspace Rust tests passed; 70 Python tests passed. Workspace build, formatting, Clippy, and Settings configuration validation passed. Opt-in native desktop checks were not rerun because Weston is absent.

Related: #5.

shell/ferese-shell/src/status_ui/lifecycle.rs

@@ -39,7 +39,8 @@ impl OpenMenu {
 
 impl FereseShell {
     pub fn open_menu(&mut self, kind: Menu, anchor: PopoverAnchor) -> Task<Message> {
-        if !anchor.belongs_to(&self.config.panels[0])
+        if (self.snapshot.binding_mode.is_some() && anchor.item.is_some())
+            || !anchor.belongs_to(&self.config.panels[0])
             || !self.outputs.iter().any(|output| output.bar == anchor.parent)
             || self.bar_hidden(anchor.parent)
             || !kind.available(&self.status)