fix: mobile nav spacing + safe area, PDF viewer mobile layout

- Mobile nav: tighter spacing, safe-area-inset-bottom padding
- Nav items closer together so bottom section stays visible
- Nav sheet scrollable if content overflows
- PDF viewer mobile: 55vh for PDF, rest for sidebar (scrollable)
- Full screen on mobile (no border-radius, no padding)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend-v2/src/lib/components/layout/AppShell.svelte

@@ -557,22 +557,33 @@
 		top: 0;
 		left: 0;
 		bottom: 0;
-		width: min(320px, 86vw);
+		width: min(300px, 82vw);
-		padding: 18px 16px;
+		padding: 16px 14px;
+		padding-bottom: calc(16px + env(safe-area-inset-bottom, 0px));
 		background: linear-gradient(180deg, rgba(250, 246, 239, 0.96), rgba(244, 237, 228, 0.94));
 		border-right: 1px solid var(--shell-line);
 		backdrop-filter: blur(20px);
 		z-index: 40;
 		display: flex;
 		flex-direction: column;
-		gap: 18px;
+		gap: 12px;
+		overflow-y: auto;
+	}
+	.mobile-nav-list {
+		flex: 1;
+		display: flex;
+		flex-direction: column;
+		gap: 2px;
+	}
+	.mobile-nav-list a {
+		padding: 10px 12px;
 	}
-	.mobile-nav-list { flex: 1; }
 	.mobile-nav-bottom {
 		display: grid;
-		gap: 10px;
+		gap: 8px;
-		padding-top: 14px;
+		padding-top: 12px;
 		border-top: 1px solid var(--shell-line);
+		flex-shrink: 0;
 	}
 
 	.mobile-nav-head {

frontend-v2/src/lib/pages/brain/AtelierBrainPage.svelte

@@ -1385,8 +1385,8 @@
     .brain-layout { margin: 0; }
     .masonry { columns: 1; }
     .detail-sheet { width: 100%; padding: 20px; }
-    .viewer-overlay { padding: 12px; }
+    .viewer-overlay { padding: 0; }
-    .viewer-layout { grid-template-columns: 1fr; grid-template-rows: 1fr auto; width: 100%; height: 90vh; border-radius: 18px; }
+    .viewer-layout { grid-template-columns: 1fr; grid-template-rows: 55vh 1fr; width: 100%; height: 100vh; border-radius: 0; max-width: 100%; }
-    .viewer-sidebar { max-height: 40vh; border-left: none; border-top: 1px solid rgba(35,26,17,0.08); }
+    .viewer-sidebar { max-height: none; border-left: none; border-top: 1px solid rgba(35,26,17,0.08); overflow-y: auto; }
   }
 </style>