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_hash_conflicts_templ.go

@@ -367,7 +367,7 @@ func AdminHashConflicts(user User, conflicts []HashConflictData) templ.Component
 			templ_7745c5c3_Var18 = templ.NopComponent
 		}
 		ctx = templ.ClearChildren(ctx)
-		templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 27, "<!doctype html><html lang=\"en\"><head><meta charset=\"UTF-8\"><title>Hash Conflicts - Bookhoard</title><link href=\"/static/style.css\" rel=\"stylesheet\"><link rel=\"icon\" type=\"image/svg+xml\" href=\"/static/favicon.svg\"></head>")
+		templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 27, "<!doctype html><html lang=\"en\"><head><meta charset=\"UTF-8\"><meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\"><title>Hash Conflicts - Bookhoard</title><link href=\"/static/style.css\" rel=\"stylesheet\"><link rel=\"icon\" type=\"image/svg+xml\" href=\"/static/favicon.svg\"></head>")
 		if templ_7745c5c3_Err != nil {
 			return templ_7745c5c3_Err
 		}