refactor(cuesheet): images are referenced by link only

A path to a local file resolves on the machine running ontime, but not
for the clients we serve the cuesheet to, so we no longer accept it.

Validation now parses the value as a URL and checks the protocol, which
also rejects malformed values that the previous prefix check let through.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CKXcDrZoQXbJpaXiLi1aff

apps/client/src/views/cuesheet/__tests__/EditableImage.test.ts

@@ -3,20 +3,22 @@ import { describe, expect, test } from 'vitest';
 import { isValidImageSource } from '../cuesheet-table/cuesheet-table-elements/EditableImage';
 
 describe('isValidImageSource()', () => {
-  test('accepts images hosted elsewhere', () => {
+  test('accepts links to a hosted image', () => {
     expect(isValidImageSource('https://example.com/image.png')).toBe(true);
     expect(isValidImageSource('http://example.com/image.png')).toBe(true);
   });
 
-  test('accepts images served by ontime', () => {
-    expect(isValidImageSource('/user/image.png')).toBe(true);
-    expect(isValidImageSource('/external/image.png')).toBe(true);
+  test('rejects references to a local file, they would not resolve for our clients', () => {
+    expect(isValidImageSource('/user/image.png')).toBe(false);
+    expect(isValidImageSource('user/image.png')).toBe(false);
+    expect(isValidImageSource('file:///Users/me/image.png')).toBe(false);
+    expect(isValidImageSource('C:\\images\\image.png')).toBe(false);
   });
 
   test('rejects values which would not resolve to an image', () => {
     expect(isValidImageSource('www.example.com/image.png')).toBe(false);
     expect(isValidImageSource('example.com/image.png')).toBe(false);
-    expect(isValidImageSource('user/image.png')).toBe(false);
+    expect(isValidImageSource('https://')).toBe(false);
     expect(isValidImageSource('some text')).toBe(false);
   });
 });

apps/client/src/views/cuesheet/cuesheet-table/cuesheet-table-elements/EditableImage.tsx

@@ -16,11 +16,16 @@ interface EditableImageProps {
 export default memo(EditableImage);
 
 /**
- * An image is either hosted somewhere else
- * or served by ontime itself (eg. a file placed in the user folder)
+ * Images are referenced by link: anything local to the machine running ontime
+ * would not resolve for the clients we serve the cuesheet to
  */
 export function isValidImageSource(value: string): boolean {
-  return value.startsWith('http://') || value.startsWith('https://') || value.startsWith('/');
+  try {
+    const url = new URL(value);
+    return url.protocol === 'http:' || url.protocol === 'https:';
+  } catch {
+    return false;
+  }
 }
 
 function EditableImage({ initialValue, fieldLabel, readOnly, updateValue }: EditableImageProps) {
@@ -73,7 +78,7 @@ function EditableImage({ initialValue, fieldLabel, readOnly, updateValue }: Edit
             }
           }}
         />
-        {isRejected && <span className={style.message}>Use a link (https://...) or a file in ontime (/user/...)</span>}
+        {isRejected && <span className={style.message}>Images are referenced by link (https://...)</span>}
       </>
     );
   }