fix(wechat): repair share preview on disk for sanitized delivery artifacts

Production WeChat delivery strips localPath from artifacts, so share-preview
auto-repair never wrote back to HTML. Resolve paths via publishDir +
relativePath, repair at materialize and delivery prep, and pass h5Root from
Portal so page.generate can patch missing meta before sending links.

Co-authored-by: Cursor <cursoragent@cursor.com>

mindspace-wechat-html-delivery.test.mjs

@@ -81,17 +81,16 @@ test('MindSpace prepares WeChat HTML delivery with logical artifacts only', (t)
       },
     });
 
-  assert.equal(
-    fs.readFileSync(
-      path.join(
-        publishDir,
-        'public',
-        'hello.html',
-      ),
-      'utf8',
+  const written = fs.readFileSync(
+    path.join(
+      publishDir,
+      'public',
+      'hello.html',
     ),
-    content,
+    'utf8',
   );
+  assert.match(written, /name="description"/);
+  assert.match(written, /data-mindspace-page-tag="platform-brand"/);
   assert.equal(
     result.confirmedArtifacts.length,
     1,
@@ -107,12 +106,12 @@ test('MindSpace prepares WeChat HTML delivery with logical artifacts only', (t)
       isStub: false,
       isHtmlDocument: true,
       sharePreview: {
-        ok: false,
-        reason: 'missing_description',
+        ok: true,
+        reason: null,
       },
       auxiliary: false,
       sizeBytes:
-        Buffer.byteLength(content),
+        Buffer.byteLength(written),
     },
   );
   assert.equal(