feat(msgviewer): re-enable composite renderer with scroll support and inline images

Composite mode now handles j/k/g/G/PgUp/PgDown/mouse wheel for scrolling.
Text uses the configured default style. Images render inline via Vaxis.
Emails without images still use the standard pager path.

app/compositeview.go

@@ -186,13 +186,16 @@ func (cc *compositeContent) CleanupFiles() {
 }
 
 // Draw renders the composite content into the given UI context.
-// scroll is the row offset from the top.
-func (cc *compositeContent) Draw(ctx *ui.Context, scroll int) {
+// scroll is the row offset from the top. style is the default text style.
+func (cc *compositeContent) Draw(ctx *ui.Context, scroll int, style ...vaxis.Style) {
 	width := ctx.Width()
 	height := ctx.Height()
 	row := -scroll // start above viewport if scrolled
 
 	defaultStyle := vaxis.Style{}
+	if len(style) > 0 {
+		defaultStyle = style[0]
+	}
 
 	for _, b := range cc.blocks {
 		switch b.blockType {