feat: multi-media attachments, linkify URLs, shared MessageMediaGrid

- Add media_items array support to ticket messages (types, API clients)
- Create shared MessageMediaGrid component with photo grid, fullscreen
  viewer, keyboard nav, video/document rendering
- Replace per-page AdminMessageMedia/MessageMedia with MessageMediaGrid
- Add linkifyText util (DOMPurify-sanitized) for auto-linking URLs
- Support multi-file upload (up to 10) in AdminTickets and Support pages
- Remove unused ticketsApi import from AdminUserDetail

src/utils/linkify.ts

@@ -0,0 +1,28 @@
+import DOMPurify from 'dompurify';
+
+/**
+ * Match http(s) URLs but exclude common trailing punctuation that is unlikely
+ * to be part of the URL itself (e.g. the period at the end of a sentence,
+ * or a closing bracket / quote that wraps the URL).
+ */
+const URL_REGEX = /(https?:\/\/[^\s<]+[^\s<.,;:!?\])}"'])/g;
+
+/**
+ * Linkify plain text by wrapping http(s) URLs in <a> tags.
+ * Returns an HTML string sanitized via DOMPurify with a strict allowlist
+ * (only <a> + <br>), safe to render in the UI.
+ *
+ * Trailing punctuation (.,;:!?)]}"') is excluded from the URL match so a
+ * sentence like `Visit https://example.com.` does not capture the period.
+ */
+export function linkifyText(text: string | null | undefined): string {
+  if (!text) return '';
+  const replaced = text.replace(
+    URL_REGEX,
+    '<a href="$1" target="_blank" rel="noopener noreferrer">$1</a>',
+  );
+  return DOMPurify.sanitize(replaced, {
+    ALLOWED_TAGS: ['a', 'br'],
+    ALLOWED_ATTR: ['href', 'target', 'rel'],
+  });
+}