fix(web): viewport meta on all admin/profile pages; admin users page reworked for mobile

- The desktop-on-Android bug: 8 page templates (admin, admin_settings,
  admin_users, admin_library, admin_archived, admin_hash_conflicts,
  admin_processing_issues, profile) lacked the viewport meta, so mobile
  browsers fell back to a ~980px layout viewport and rendered the
  desktop layout. Added the same meta the other 21 pages already had —
  partials without a head were skipped deliberately.
- Admin Users page: the create-user form no longer dominates the page —
  it is hidden behind an explicit '+ Create User' button (Alpine
  x-show/x-cloak, the site-wide convention) with a Close control.
- The user list is responsive: table on md+, stacked per-user cards
  below. Role/delete controls are shared partials with DOM-id suffixes
  so both renderings keep unique swap targets (last-admin protections
  preserved in both).

templates/admin.templ

@@ -5,6 +5,7 @@ templ Admin(user User, stats AdminStats) {
 	<html lang="en">
 		<head>
 			<meta charset="UTF-8"/>
+			<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
 			<title>Admin Dashboard - Bookhoard</title>
 			<link href="/static/style.css" rel="stylesheet"/>
 			<link rel="icon" type="image/svg+xml" href="/static/favicon.svg"/>