Narrow relative link handling to only ../ paths

Per maintainer feedback, restrict the click interception to links
starting with "../" only. Remove the now-unnecessary isRelativePath()
utility and its test file.

Agent-Logs-Url: https://github.com/MarkEdit-app/MarkEdit-preview/sessions/bf2367cc-cfbf-4aab-8991-df30b8f2a973

Co-authored-by: cyanzhong <6745066+cyanzhong@users.noreply.github.com>

Author: Copilot

src/utils.ts

@@ -90,20 +90,6 @@ export function joinPaths(path1: string, path2: string) {
   return path1 + '/' + path2;
 }
 
-export function isRelativePath(href: string) {
-  // Anchor links
-  if (href.startsWith('#')) {
-    return false;
-  }
-
-  // Absolute URLs (http:, https:, mailto:, data:, etc.) or protocol-relative URLs
-  if (/^([a-z][a-z0-9+.-]*:|\/\/)/i.test(href)) {
-    return false;
-  }
-
-  return true;
-}
-
 export function stripQuotes(input: string) {
   if ((input.startsWith('"') && input.endsWith('"')) || (input.startsWith("'") && input.endsWith("'"))) {
     return input.slice(1, -1);

src/view.ts

@@ -1,5 +1,5 @@
 import { MarkEdit } from 'markedit-api';
-import { appendStyle, getFileExtension, getFileName, isRelativePath, joinPaths, selectFullRange } from './utils';
+import { appendStyle, getFileExtension, getFileName, joinPaths, selectFullRange } from './utils';
 import { renderMarkdown, renderMermaid, renderKatex, handlePostRender, applyStyles } from './render';
 import { replaceImageURLs } from './image';
 import { hidePreviewButtons, previewModes } from './settings';
@@ -77,7 +77,7 @@ export function setUp() {
 
     // Use getAttribute to get the raw href, not the resolved absolute URL
     const href = anchor.getAttribute('href');
-    if (href === null || href === '' || !isRelativePath(href)) {
+    if (!href?.startsWith('../')) {
       return;
     }