fix(layout): restore Zibll float dual-column so content no longer overlaps sidebar

Align main shells to main.container > .content-wrap + .sidebar siblings, drop
content-shell padding on dual-column hosts, and remove route flex overrides that
disabled the negative-margin sidebar math.

assets/css/routes/user-auth.css

@@ -77,13 +77,4 @@
 	color: #e74c3c;
 }
 
-.page-template-user-auth .content-wrap {
-	display: flex;
-	gap: 20px;
-	flex-wrap: wrap;
-}
-
-.page-template-user-auth .content-layout {
-	flex: 1 1 0;
-	min-width: 0;
-}
+/* Dual-column geometry owned by layout.css site-layout float rules (Zibll). */