refactor: phase 4 cleanup — delete SidebarLayout, drop dashboard-body

Now that all member-area pages have migrated to PageShell +
ColumnsLayout, SidebarLayout has no consumers and can be deleted.
PageShell owns the flex chain, so the .dashboard-body wrapper on
member/dashboard.vue (flex: 1; display: flex; flex-direction: column;
min-height: 0) is redundant. Update stale SidebarLayout comments on
members/[id].vue to reference ColumnsLayout.

app/pages/member/dashboard.vue

@@ -27,9 +27,8 @@
       <!-- Dashboard Content -->
       <template v-else>
         <ColumnsLayout cols="events-sidebar" :limit="5">
-          <div class="dashboard-body">
-            <!-- Member Status Banner -->
-            <MemberStatusBanner />
+          <!-- Member Status Banner -->
+          <MemberStatusBanner />
 
             <!-- Welcome Header -->
             <PageHeader :title="`Welcome back, ${memberData?.name || ''}`">
@@ -202,7 +201,6 @@
                 </DashedBox>
               </div>
             </div>
-          </div>
         </ColumnsLayout>
       </template>
 
@@ -451,13 +449,6 @@ useHead({
   margin-top: 8px;
 }
 
-.dashboard-body {
-  flex: 1;
-  display: flex;
-  flex-direction: column;
-  min-height: 0;
-}
-
 .content-row {
   display: grid;
   grid-template-columns: repeat(2, minmax(0, 1fr));

app/pages/members/[id].vue

@@ -15,7 +15,7 @@
     <!-- Profile Content -->
     <template v-else>
 
-      <!-- HERO: full-bleed, outside SidebarLayout -->
+      <!-- HERO: full-bleed, outside ColumnsLayout -->
       <div class="profile-hero" :class="{ 'profile-hero--with-links': hasSocialLinks }">
 
         <!-- Left: Avatar + Identity -->
@@ -514,7 +514,7 @@ useHead({
 }
 
 /* ====================================================
-   SECTIONS — inside SidebarLayout
+   SECTIONS — inside ColumnsLayout
    ==================================================== */
 
 .profile-section {
@@ -734,7 +734,7 @@ useHead({
    ==================================================== */
 
 @media (max-width: 1024px) {
-  /* SidebarLayout sidebar hides itself at ≤1024px */
+  /* ColumnsLayout events-sidebar hides itself at ≤1024px */
   .profile-two-col {
     grid-template-columns: 1fr;
   }