[web] Add #main-content to some pug pages (fix skip-to-content links) (#18050)

* Add `#main-content` to some pug pages

This fixes our `skip-to-content` accessibility anchor links. Alternatively or additionally, we can set `suppressSkipToContent = true` in some pages: that will remove the anchor link in the page.

While working on this, I noticed that sometimes we still have a bit of extra nesting or components that should maybe be out of `<main>` or `#main-content`. In a future PR we can maybe update these elements to target the "real core content" of the page.

* Add `suppressSkipToContent` in confirm-email page

GitOrigin-RevId: 6cbf4112f2d1a2d8eff06f142d0c2b4f3a5d9cff

services/web/modules/launchpad/app/views/launchpad.pug

@@ -31,7 +31,7 @@ block append meta
 block content
 	script(type="text/javascript", nonce=scriptNonce, src=(wsUrl || '/socket.io') + '/socket.io.js')
 
-	.content.content-alt
+	.content.content-alt#main-content
 		.container(ng-cloak)
 			.row
 				.col-md-8.col-md-offset-2

services/web/modules/user-activate/app/views/user/register.pug

@@ -5,7 +5,6 @@ block entrypointVar
 
 
 block content
-	.content.content-alt
+	.content.content-alt#main-content
 		.container
 			#user-activate-register-container
-