make divider draggable + add space/h keys actions

layout.go

@@ -0,0 +1,47 @@
+package main
+
+// Layout constants to avoid magic numbers
+const (
+	minFsTreeWidth   = 5
+	minNoteViewWidth = 10
+	dividerWidth     = 1
+	dragHitArea      = 2 // +/- chars around divider
+)
+
+// calculateLayout computes the widths for the file tree and note view
+// based on the terminal dimensions and the desired tree width.
+// It returns the constrained tree width and the resulting note view width.
+func calculateLayout(totalWidth, requestedTreeWidth int) (treeWidth, noteWidth int) {
+	treeWidth = requestedTreeWidth
+	
+	// Default initial width if not set
+	if treeWidth == 0 {
+		treeWidth = totalWidth / 4
+	}
+
+	// Calculate maximum allowed width for the tree
+	// Total width - divider - minimum note view width
+	maxTreeWidth := totalWidth - dividerWidth - minNoteViewWidth
+
+	// Apply constraints
+	if treeWidth > maxTreeWidth {
+		treeWidth = maxTreeWidth
+	}
+	if treeWidth < minFsTreeWidth {
+		treeWidth = minFsTreeWidth
+	}
+
+	noteWidth = totalWidth - treeWidth - dividerWidth
+	
+	// Safety check to ensure noteWidth is never negative
+	if noteWidth < 0 {
+		noteWidth = 0
+	}
+
+	return treeWidth, noteWidth
+}
+
+// isHoveringDivider checks if the mouse cursor is within the interaction area of the divider
+func isHoveringDivider(mouseX, dividerPos int) bool {
+	return mouseX >= dividerPos-dragHitArea && mouseX <= dividerPos+dragHitArea
+}