Give popup panels their full width whenever the window has room for it

The width of a popup panel was a ratio of the window's width, capped at
the panel's maximum. The ratio never did anything for confirmations and
prompts, whose minimum and maximum widths are both 80; they always came
out at 80, or at the window width if that was narrower. For menus and
the commit message editor it meant that the window had to be 158 columns
wide before either of them reached its maximum width, and that below 140
columns they were 80 columns wide. This is narrower than the window has
room for, and too narrow for the three columns of the recent repos menu.

Give every panel the width it asks for as long as it fits, and shrink it
only when the window leaves no choice. A panel keeps a margin of three
columns on either side while it can afford to, so that it doesn't sit
flush against the sides of the window as soon as the window gets a
little narrow.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

pkg/gui/controllers/helpers/confirmation_helper.go

@@ -127,18 +127,28 @@ func (self *ConfirmationHelper) getPopupPanelDimensionsAux(contentWidth int, con
 		height/2 + panelHeight/2 - 1
 }
 
+const (
+	// The width a popup panel keeps as long as it fits into the window at all,
+	// even when the panel asks for less.
+	popupPanelMinWidth = 80
+
+	// The margin we try to leave between a popup panel and the sides of the
+	// window, so that the panel doesn't sit flush against them as soon as the
+	// window gets a little narrow.
+	popupPanelMargin = 3
+)
+
 // Returns the outer width of the view, including its frame. To decide how to wrap text, subtract 2.
 // Also, note that X1-X0 of the view is one less than this.
-func (self *ConfirmationHelper) getPopupPanelWidth(maxWidth int) int {
-	width, _ := self.c.GocuiGui().Size()
-	// we want a minimum width up to a point, then we do it based on ratio, but only up to the given max width
-	panelWidth := min(4*width/7, maxWidth)
-	minWidth := 80
-	if panelWidth < minWidth {
-		panelWidth = min(width-2, minWidth)
-	}
+func (self *ConfirmationHelper) getPopupPanelWidth(requestedWidth int) int {
+	windowWidth, _ := self.c.GocuiGui().Size()
+	// A panel gets the width it asks for as long as the margin fits beside it.
+	// It gives the margin up before it goes below the minimum width, and a
+	// column on either side is all it leaves in the end.
+	widthWithMargin := windowWidth - 2*popupPanelMargin
+	widthAtMinWidth := min(popupPanelMinWidth, windowWidth-2)
 
-	return panelWidth
+	return min(requestedWidth, max(widthWithMargin, widthAtMinWidth))
 }
 
 func (self *ConfirmationHelper) prepareConfirmationPanel(