fix(fe): enforce single-screen viewport principle for ApprovalQueue

PRINCIPLE: First load must fit within single viewport (no scroll required,
excluding dashboard summary section).

CHANGES:
1. ReviewWorkbenchLayout.vue
   - Changed: height: calc(100vh - 220px) → height: 100%
   - Reason: calc() was hardcoded to fixed pixels, not respecting parent flex layout
   - Added: min-height: 0 (critical for flex overflow behavior)

2. ApprovalQueue.vue (.content)
   - Added: height: 100% + min-height: 0

3. ApprovalQueue.vue (.detail-panel)
   - Removed: max-height: 700px (was hard limit, causing overflow)
   - Added: height: 100% + min-height: 0

RESULT: Page now fits single viewport without scroll.
Individual panels (list, detail) maintain internal scroll as needed.

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

frontend/src/features/approval/pages/ApprovalQueue.vue

@@ -403,6 +403,8 @@ h3 {
   display: grid;
   grid-template-columns: 350px 1fr;
   gap: var(--spacing-5);
+  height: 100%;
+  min-height: 0;
 }
 
 .request-list {
@@ -489,7 +491,8 @@ h3 {
   border-radius: var(--border-radius-lg);
   padding: var(--spacing-4);
   background: var(--color-background-secondary);
-  max-height: 700px;
+  height: 100%;
+  min-height: 0;
   overflow-y: auto;
 }