feat(server): add discover card DTO helpers

Made-with: Cursor

server/constants/discover-list.ts

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+/** 发现页用户列表每页条数（与公开列表一致） */
+export const DISCOVER_LIST_PAGE_SIZE = 10;

server/utils/discover-card.test.ts

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+import { describe, expect, test } from "bun:test";
+import { discoverCardAvatarUrl, discoverCardLocationLine } from "./discover-card";
+
+describe("discoverCardAvatarUrl", () => {
+  test("returns null when visibility is not public", () => {
+    expect(discoverCardAvatarUrl("https://x/a.png", "private")).toBeNull();
+    expect(discoverCardAvatarUrl("https://x/a.png", "unlisted")).toBeNull();
+  });
+
+  test("returns null when avatar empty", () => {
+    expect(discoverCardAvatarUrl(null, "public")).toBeNull();
+    expect(discoverCardAvatarUrl("  ", "public")).toBeNull();
+  });
+
+  test("returns trimmed url when public", () => {
+    expect(discoverCardAvatarUrl(" https://x/a.png ", "public")).toBe("https://x/a.png");
+  });
+});
+
+describe("discoverCardLocationLine", () => {
+  test("returns null when show flag false or text empty", () => {
+    expect(discoverCardLocationLine(true, false, "北京")).toBeNull();
+    expect(discoverCardLocationLine(true, true, "")).toBeNull();
+    expect(discoverCardLocationLine(true, true, "  ")).toBeNull();
+  });
+
+  test("returns trimmed text when allowed", () => {
+    expect(discoverCardLocationLine(true, true, " 上海 ")).toBe("上海");
+  });
+});

server/utils/discover-card.ts

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+export function discoverCardAvatarUrl(
+  avatar: string | null | undefined,
+  avatarVisibility: string,
+): string | null {
+  if (avatarVisibility !== "public") {
+    return null;
+  }
+  const t = typeof avatar === "string" ? avatar.trim() : "";
+  return t.length > 0 ? t : null;
+}
+
+export function discoverCardLocationLine(
+  discoverVisible: boolean,
+  discoverShowLocation: boolean,
+  discoverLocation: string | null | undefined,
+): string | null {
+  if (!discoverVisible || !discoverShowLocation) {
+    return null;
+  }
+  const t = typeof discoverLocation === "string" ? discoverLocation.trim() : "";
+  return t.length > 0 ? t : null;
+}