feat: close button (X) in panel title bar

Renders an X glyph in the top-right of every panel's title bar; left-
click on it calls M.close(). Hit-test in _dispatch_event runs before
the widget-forward path so the click is consumed by the panel-frame
even when a widget would otherwise handle it. Pairs with the existing
ESC-close-pattern that lives at module level.

init.lua

@@ -141,7 +141,35 @@ end
 
 --- _dispatch_event(event): route a synthetic or real input event.
 --- event = {kind="click", x, y, button="left"|"right"} or {kind="wheel", dy}
+-- Close-button rect in the top-right of the title bar. Same math is used
+-- by render() (draw the × glyph) and _dispatch_event (hit-test left-click).
+local function close_button_rect(panel_x, panel_y, panel_w, padding, font_size_title)
+    local size = font_size_title + padding
+    return {
+        x = panel_x + panel_w - size - padding,
+        y = panel_y + padding,
+        w = size,
+        h = size,
+    }
+end
+
 local function _dispatch_event(event)
+    -- Close-button intercept (top-right ×): left-click closes the active panel
+    -- before the click is forwarded to the widget or context-menu.
+    if active and event.kind == "click" and event.button == "left" then
+        local screen_w, screen_h = get_screen_size()
+        local panel_w = screen_w * theme.panel_width_frac
+        local panel_h = screen_h * theme.panel_height_frac
+        local panel_x = (screen_w - panel_w) / 2
+        local panel_y = (screen_h - panel_h) / 2
+        local cb = close_button_rect(panel_x, panel_y, panel_w, theme.padding, theme.font_size_title)
+        if event.x >= cb.x and event.x < cb.x + cb.w
+           and event.y >= cb.y and event.y < cb.y + cb.h then
+            M.close()
+            return
+        end
+    end
+
     -- Context-menu intercept: any click is consumed by the menu.
     if ctx_menu and event.kind == "click" then
         -- Hit-test rows
@@ -475,6 +503,14 @@ function M.render()
                             theme.font_size_title,
                             theme.text_color)
 
+    -- Close button (×) in top-right of title bar. Hit-tested in _dispatch_event.
+    local cb = close_button_rect(panel_x, panel_y, panel_w, padding, theme.font_size_title)
+    engine.render.draw_text("X",
+                            cb.x + math.floor(cb.w / 4),
+                            cb.y,
+                            theme.font_size_title,
+                            theme.text_color)
+
     -- Content area (below title bar)
     local title_area_h = theme.font_size_title + padding * 2
     local content_bounds = {