feat: enhance PDF comparison with new change types and zoom functionality

- Added support for 'moved' and 'style-changed' change types in PDF comparison.
- Implemented category filters for changes, allowing users to filter by text, images, headers, annotations, formatting, and background.
- Introduced zoom functionality with buttons for zooming in, out, and resetting to default.
- Updated UI to reflect new change types and categories, including visual indicators for moved and style-changed items.
- Enhanced summary display to include counts for moved and style-changed changes.
- Refactored rendering logic to accommodate zoom levels and improve performance.
- Added tests for new change detection features and category assignments.

src/js/compare/worker-api.ts

@@ -0,0 +1,90 @@
+import type {
+  CompareTextItem,
+  ComparePageSignature,
+  ComparePagePair,
+  CompareChangeSummary,
+  CompareTextChange,
+} from './types.ts';
+import { diffTextRuns } from './engine/diff-text-runs.ts';
+import { pairPages } from './engine/pair-pages.ts';
+
+let worker: Worker | null = null;
+let messageId = 0;
+const pending = new Map<
+  number,
+  { resolve: (value: unknown) => void; reject: (reason: unknown) => void }
+>();
+
+function getWorker(): Worker | null {
+  if (worker) return worker;
+  try {
+    worker = new Worker(
+      new URL('./engine/compare.worker.ts', import.meta.url),
+      { type: 'module' }
+    );
+    worker.onmessage = function (e) {
+      const { id, type, ...rest } = e.data;
+      const p = pending.get(id);
+      if (!p) return;
+      pending.delete(id);
+      if (type === 'error') {
+        p.reject(new Error((rest as { message: string }).message));
+      } else {
+        p.resolve(rest);
+      }
+    };
+    worker.onerror = function () {
+      worker?.terminate();
+      worker = null;
+      for (const [, p] of pending) {
+        p.reject(new Error('Worker crashed'));
+      }
+      pending.clear();
+    };
+    return worker;
+  } catch {
+    return null;
+  }
+}
+
+function postToWorker(msg: Record<string, unknown>): Promise<unknown> {
+  const w = getWorker();
+  if (!w) return Promise.reject(new Error('No worker'));
+  const id = ++messageId;
+  return new Promise((resolve, reject) => {
+    pending.set(id, { resolve, reject });
+    w.postMessage({ ...msg, id });
+  });
+}
+
+export async function diffTextRunsAsync(
+  beforeItems: CompareTextItem[],
+  afterItems: CompareTextItem[]
+): Promise<{ changes: CompareTextChange[]; summary: CompareChangeSummary }> {
+  try {
+    const result = (await postToWorker({
+      type: 'diff',
+      beforeItems,
+      afterItems,
+    })) as { changes: CompareTextChange[]; summary: CompareChangeSummary };
+    return result;
+  } catch {
+    return diffTextRuns(beforeItems, afterItems);
+  }
+}
+
+export async function pairPagesAsync(
+  leftPages: ComparePageSignature[],
+  rightPages: ComparePageSignature[]
+): Promise<ComparePagePair[]> {
+  try {
+    const result = (await postToWorker({
+      type: 'pair',
+      leftPages,
+      rightPages,
+    })) as { pairs: ComparePagePair[] };
+    return result.pairs;
+  } catch {
+    return pairPages(leftPages, rightPages);
+  }
+}