feat(posts): support short titles for resource cards

Add optional post-level and localized title fields, and use a new
postTitleText helper for Resource.title so card/list surfaces prefer short
backend-provided titles instead of full body text. When title is missing,
fallback to the first non-empty body line, then filename, then post id.

Document the backend handoff in docs/posts-title-api.md alongside the other
backend task docs.

src/components/messageStream/utils/postText.ts

@@ -11,3 +11,19 @@ export function postDisplayText(post: Post, lang: string): string {
     ""
   );
 }
+
+export function postTitleText(post: Post, lang: string): string {
+  const key = localizationKey(lang);
+  const localized =
+    post.localizations?.[key as keyof typeof post.localizations];
+  const explicitTitle = localized?.title?.trim() || post.title?.trim();
+  if (explicitTitle) return explicitTitle;
+
+  const text = postDisplayText(post, lang);
+  return (
+    text
+      .split(/\n{1,}/)
+      .map((line) => line.trim())
+      .find(Boolean) || ""
+  );
+}

src/types/post.ts

@@ -14,6 +14,9 @@ export type PostTypeFilter = PostType | "all";
 export type AttachmentKind = "image" | "video" | "document";
 
 export type PostLocaleTexts = {
+  /** Short display title for list/card surfaces. */
+  title?: string;
+  /** Full post body text. */
   text: string;
 };
 
@@ -59,6 +62,8 @@ export type Post = {
   categorySlug: string;
   language: string;
   sourceLanguage?: string;
+  /** Short display title for list/card surfaces. */
+  title?: string;
   text?: string;
   localizations?: Partial<PostLocalizations>;
   attachments: Attachment[];

src/utils/postResourceAdapter.ts

@@ -1,6 +1,9 @@
 import type { Category, Resource } from "../api";
 import type { Attachment, Post } from "../types/post";
-import { postDisplayText } from "../components/messageStream/utils/postText";
+import {
+  postDisplayText,
+  postTitleText,
+} from "../components/messageStream/utils/postText";
 
 export type PostBackedResource = Resource & {
   downloadPostId?: string;
@@ -35,7 +38,7 @@ export function postToResource(
   categories: Category[] = [],
 ): PostBackedResource {
   const first = post.attachments[0];
-  const title = postDisplayText(post, lang) || first?.filename || post.id;
+  const title = postTitleText(post, lang) || first?.filename || post.id;
   const category = categories.find((c) => c.id === post.categoryId);
   return {
     id: post.id,