feat(v2): add tiling layout, sidebar controls, and keyboard shortcuts

- TilingGrid: dynamic CSS Grid with auto-preset based on pane count
- Layout presets: 1-col, 2-col, 3-col, 2x2, master-stack
- PaneContainer: close button, status indicator, focus highlight
- SessionList: new terminal button, layout preset selector, pane list
- Layout store: pane CRUD, focus management, grid template generation
- Keyboard: Ctrl+N new terminal, Ctrl+1-4 focus pane by index

v2/src/lib/components/Layout/PaneContainer.svelte

@@ -3,15 +3,25 @@
 
   interface Props {
     title: string;
+    status?: 'idle' | 'running' | 'error' | 'done';
+    onClose?: () => void;
     children: Snippet;
   }
 
-  let { title, children }: Props = $props();
+  let { title, status = 'idle', onClose, children }: Props = $props();
 </script>
 
 <div class="pane-container">
   <div class="pane-header">
     <span class="pane-title">{title}</span>
+    <div class="pane-controls">
+      {#if status !== 'idle'}
+        <span class="status {status}">{status}</span>
+      {/if}
+      {#if onClose}
+        <button class="close-btn" onclick={onClose} title="Close pane">&times;</button>
+      {/if}
+    </div>
   </div>
   <div class="pane-content">
     {@render children()}
@@ -26,12 +36,14 @@
     border-radius: var(--border-radius);
     overflow: hidden;
     border: 1px solid var(--border);
+    height: 100%;
   }
 
   .pane-header {
     height: var(--pane-header-height);
     display: flex;
     align-items: center;
+    justify-content: space-between;
     padding: 0 10px;
     background: var(--bg-tertiary);
     border-bottom: 1px solid var(--border);
@@ -47,8 +59,39 @@
     text-overflow: ellipsis;
   }
 
+  .pane-controls {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+  }
+
+  .status {
+    font-size: 10px;
+    padding: 1px 5px;
+    border-radius: 3px;
+  }
+
+  .status.running { color: var(--ctp-blue); }
+  .status.error { color: var(--ctp-red); }
+  .status.done { color: var(--ctp-green); }
+
+  .close-btn {
+    background: none;
+    border: none;
+    color: var(--text-muted);
+    font-size: 16px;
+    cursor: pointer;
+    padding: 0 2px;
+    line-height: 1;
+  }
+
+  .close-btn:hover {
+    color: var(--ctp-red);
+  }
+
   .pane-content {
     flex: 1;
-    overflow: auto;
+    overflow: hidden;
+    min-height: 0;
   }
 </style>