fix(ui): fully dim dashboard when help overlay is shown

When the help overlay was displayed on top of the dashboard, only the
intersecting region appeared dimmed. The root cause: cancelFaint injects
\033[22m (normal intensity) into each overlay line to keep it bright,
and these codes survived into the composited result. A subsequent
dimBackground pass couldn't override them.

Fix: dimBackground now replaces \033[22m with \033[2m before applying
its own faint, so nested overlays dim the entire background uniformly.

Closes #146

Author: cpcloud

internal/app/view.go

@@ -949,6 +949,10 @@ func (m *Model) tableView(tab *Tab) string {
 // the dim state.
 func dimBackground(s string) string {
 	dimmed := strings.ReplaceAll(s, "\033[0m", "\033[0;2m")
+	// Neutralize cancel-faint markers left by a previous cancelFaint pass
+	// (nested overlays). Without this, \033[22m codes embedded in an
+	// earlier overlay's content would override the dim we're applying.
+	dimmed = strings.ReplaceAll(dimmed, "\033[22m", "\033[2m")
 	lines := strings.Split(dimmed, "\n")
 	for i, line := range lines {
 		lines[i] = "\033[2m" + line

internal/app/view_test.go

@@ -620,3 +620,17 @@ func TestHeaderTitleWidth(t *testing.T) {
 		})
 	}
 }
+
+func TestDimBackgroundNeutralizesCancelFaint(t *testing.T) {
+	// Simulate a composited overlay: cancelFaint injects \033[22m (normal
+	// intensity) so the overlay content stays bright. A subsequent
+	// dimBackground pass must neutralize those markers so the entire
+	// background dims uniformly (nested overlay scenario).
+	inner := cancelFaint("dashboard content")
+	assert.Contains(t, inner, "\033[22m", "cancelFaint should inject normal-intensity")
+
+	dimmed := dimBackground(inner)
+	assert.NotContains(t, dimmed, "\033[22m",
+		"dimBackground should neutralize cancel-faint markers from nested overlays")
+	assert.Contains(t, dimmed, "\033[2m", "dimBackground should apply faint")
+}