feat(core): Add input modes and half-page cursor movement.

crates/pikl-core/src/model/event.rs

@@ -11,6 +11,15 @@ use std::sync::Arc;
 
 use serde_json::Value;
 
+/// Input mode. Insert mode sends keystrokes to the filter,
+/// normal mode uses vim-style navigation keybinds.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub enum Mode {
+    #[default]
+    Insert,
+    Normal,
+}
+
 /// A command the menu should process. Frontends and headless
 /// scripts both produce these. The menu loop consumes them
 /// sequentially.
@@ -23,6 +32,9 @@ pub enum Action {
     MoveToBottom,
     PageUp(usize),
     PageDown(usize),
+    HalfPageUp(usize),
+    HalfPageDown(usize),
+    SetMode(Mode),
     Confirm,
     Cancel,
     Resize { height: u16 },
@@ -51,6 +63,7 @@ pub struct ViewState {
     pub filter_text: Arc<str>,
     pub total_items: usize,
     pub total_filtered: usize,
+    pub mode: Mode,
 }
 
 /// A single item in the current viewport window. Has the