fix(fe): sidebar footer alignment and scroll structure

Changes:
  • Reorganize footer: buttons first, version text below
  • Add .ks-sidebar__footer-buttons wrapper for proper layout
  • Style .ks-sidebar__version as small caption text (10px)
  • Fix sidebar scroll: sidebar overflow: hidden, nav: overflow-y: auto only
  • Add flex-shrink: 0 to footer (prevent size collapse)

This prevents:
  ✓ Nested scroll (sidebar + nav both scrolling)
  ✓ Awkward footer alignment
  ✓ Footer contributing to layout scroll

Single-scroll principle: only .nav scrolls, header/footer fixed

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

frontend/src/shared/shell/KsSidebar.vue

@@ -196,23 +196,25 @@ const sidebarClass = computed(() => ({
 
     <!-- Sidebar footer -->
     <div class="ks-sidebar__footer">
+      <div class="ks-sidebar__footer-buttons">
+        <button
+          type="button"
+          class="ks-sidebar__footer-btn"
+          title="도움말"
+        >
+          ❓
+        </button>
+        <button
+          type="button"
+          class="ks-sidebar__footer-btn"
+          title="설정"
+        >
+          ⚙️
+        </button>
+      </div>
       <div v-if="!collapsed" class="ks-sidebar__version">
         v{{ appVersion }}
       </div>
-      <button
-        type="button"
-        class="ks-sidebar__footer-btn"
-        title="도움말"
-      >
-        ❓
-      </button>
-      <button
-        type="button"
-        class="ks-sidebar__footer-btn"
-        title="설정"
-      >
-        ⚙️
-      </button>
     </div>
   </aside>
 </template>
@@ -225,8 +227,7 @@ const sidebarClass = computed(() => ({
   display: flex;
   flex-direction: column;
   transition: width 200ms cubic-bezier(0.4, 0, 0.2, 1);
-  overflow-y: auto;
-  overflow-x: hidden;
+  overflow: hidden;
   flex-shrink: 0;
 }
 
@@ -378,6 +379,21 @@ const sidebarClass = computed(() => ({
   flex-direction: column;
   gap: var(--spacing-2);
   align-items: center;
+  flex-shrink: 0;
+}
+
+.ks-sidebar__footer-buttons {
+  display: flex;
+  gap: var(--spacing-2);
+  justify-content: center;
+}
+
+.ks-sidebar__version {
+  font-size: 10px;
+  color: var(--ks-color-text-muted);
+  letter-spacing: 0.05em;
+  text-align: center;
+  line-height: 1.2;
 }
 
 .ks-sidebar__footer-btn {