Refactor SnippetLibrary and State classes for improved readability and consistency

- Updated formatting and indentation in snippets.js for better code clarity.
- Enhanced error handling and notifications in sendToActiveSession method.
- Improved variable resolution logic for command snippets.
- Added new methods for managing session state in state.js.
- Introduced new split pane functionality in terminal.js for better user experience.
- Enhanced modal handling and user notifications across various components.

frontend/src/js/commands.js

@@ -194,6 +194,20 @@ class CommandPalette {
 
         // Terminal actions (only when a session is active)
         if (this.app.state.activeSessionId) {
+            cmds.push({
+                id: 'split-vertical',
+                label: 'Split Pane Right',
+                section: 'Terminal',
+                shortcut: '⌘⇧D',
+                action: () => this.app.splitPane('vertical'),
+            });
+            cmds.push({
+                id: 'split-horizontal',
+                label: 'Split Pane Down',
+                section: 'Terminal',
+                shortcut: '⌘⇧E',
+                action: () => this.app.splitPane('horizontal'),
+            });
             cmds.push({
                 id: 'clear-terminal',
                 label: 'Clear Terminal',