Fixes #7: Rendering performance optimizations

- requestAnimationFrame batching: rerenderRpgState() now batches all
  render calls into a single animation frame, reducing reflow/repaint costs

- Lightweight change detection: Render functions use updateIfChanged() to
  skip DOM updates when content hasn't changed, and only re-bind event
  handlers when the DOM was actually updated

- CSS content-visibility: Added content-visibility: auto with
  contain-intrinsic-size to inventory and equipment containers, deferring
  rendering of off-screen content

New file: src/systems/rendering/renderUtils.js (rendering utilities module)
Updated: All render modules + sillytavern.js integration + style.css

src/systems/rendering/inventory.js

@@ -10,6 +10,7 @@ import { updateInventoryItem } from '../interaction/inventoryEdit.js';
 import { parseItems } from '../../utils/itemParser.js';
 import { isItemLocked, setItemLock } from '../generation/lockManager.js';
 import { i18n } from '../../core/i18n.js';
+import { updateIfChanged } from './renderUtils.js';
 
 // Type imports
 /** @typedef {import('../../types/inventory.js').InventoryV2} InventoryV2 */
@@ -594,13 +595,15 @@ export function renderInventory() {
 
     // Generate HTML and update DOM
     const html = generateInventoryHTML(inventory, options);
-    $inventoryContainer.html(html);
+    const domUpdated = updateIfChanged($inventoryContainer, html, 'rpg-inventory');
 
     // Restore form states after re-rendering (fixes Bug #1)
     restoreFormStates();
 
-    // Event listener for editing item names (mobile-friendly contenteditable)
-    $inventoryContainer.find('.rpg-item-name.rpg-editable').on('blur', function() {
+    // Only re-bind event handlers if DOM was actually updated
+    if (domUpdated) {
+        // Event listener for editing item names (mobile-friendly contenteditable)
+        $inventoryContainer.find('.rpg-item-name.rpg-editable').on('blur', function() {
         const field = $(this).data('field');
         const index = parseInt($(this).data('index'));
         const location = $(this).data('location');
@@ -632,6 +635,7 @@ export function renderInventory() {
         // Save settings
         saveSettings();
     });
+    } // end if (domUpdated)
 }
 
 /**