feat: add converter registry

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

test/converters/registry.test.js

@@ -0,0 +1,32 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { register, resolve, listTargetFormats, _resetForTests } from '../../src/converters/registry.js';
+
+beforeEach(() => {
+  _resetForTests();
+});
+
+describe('converter registry', () => {
+  it('resolves a registered source/target pair', () => {
+    const convert = async () => {};
+    register({ family: 'image', sourceFormat: 'png', targetFormat: 'webp', convert });
+
+    const entry = resolve('png', 'webp');
+
+    expect(entry.family).toBe('image');
+    expect(entry.convert).toBe(convert);
+  });
+
+  it('returns null for an unregistered pair', () => {
+    expect(resolve('png', 'made-up')).toBeNull();
+  });
+
+  it('lists all target formats registered for a source format', () => {
+    register({ family: 'image', sourceFormat: 'png', targetFormat: 'webp', convert: async () => {} });
+    register({ family: 'image', sourceFormat: 'png', targetFormat: 'jpg', convert: async () => {} });
+    register({ family: 'document', sourceFormat: 'docx', targetFormat: 'pdf', convert: async () => {} });
+
+    expect(listTargetFormats('png').sort()).toEqual(['jpg', 'webp']);
+    expect(listTargetFormats('docx')).toEqual(['pdf']);
+    expect(listTargetFormats('unknown-format')).toEqual([]);
+  });
+});