tui: move view mode state

crates/tui/src/view_mode.rs

@@ -0,0 +1,29 @@
+/// Display density for the history view.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Mode {
+    /// Every block fully expanded.
+    Detail,
+    /// Completed blocks compressed to roughly 5–6 lines; in-progress
+    /// tool blocks stay in detail.
+    Normal,
+    /// Each block rendered as a single line.
+    Overview,
+}
+
+impl Mode {
+    pub fn cycle(self) -> Self {
+        match self {
+            Mode::Detail => Mode::Normal,
+            Mode::Normal => Mode::Overview,
+            Mode::Overview => Mode::Detail,
+        }
+    }
+
+    pub fn label(self) -> &'static str {
+        match self {
+            Mode::Detail => "detail",
+            Mode::Normal => "normal",
+            Mode::Overview => "overview",
+        }
+    }
+}