feat(chronik): render commentPreview in ChronikRow; add aria-label for screen readers

Replace the „…" placeholder with {item.commentPreview ?? '„…"'}. Plain-text
binding — no {@html} — as specified in the security note from issue #285.
Adds aria-label to the <a> wrapper for COMMENT_ADDED rows that carry a preview,
giving screen reader users the full context in one announcement.

Generated api.ts updated manually to include commentPreview?:string; will be
regenerated by npm run generate:api once the backend is running.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/generated/api.ts

@@ -2402,6 +2402,8 @@ export interface components {
              * @description Annotation associated with the comment; populated only for COMMENT_ADDED and MENTION_CREATED kinds.
              */
             annotationId?: string;
+            /** @description Plain-text preview of the comment body (HTML stripped server-side, truncated to 120 chars); null for non-comment feed items or deleted comments. */
+            commentPreview?: string;
         };
         InvitePrefillDTO: {
             firstName: string;