feat(ui): optional gender radio in the people form and 个人资料 (T2)

One ProfileGenderField (女 / 男 / 不填, 44px, one hint line) in the
people-archive edit form (saved with the form, 不填 → null) and in
设置 → 个人资料 for the owner (saves on its own PATCH; birth-data saves never
send gender). The detail card shows 性别 (未填 when empty). Not asked in
onboarding. DESIGN/VOICE updated; 390/1280 screenshots with fictional data.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017eEAG8HD3mm8gsKXgk8uU8

frontend/src/lib/profile-gender.ts

@@ -35,3 +35,9 @@ export function profileGenderLabel(value: unknown): string {
   const gender = parseProfileGender(value);
   return gender ? PROFILE_GENDER_LABELS[gender] : PROFILE_GENDER_EMPTY_LABEL;
 }
+
+/** The account's raw profile object with the saved gender (null = not filled). */
+export function withSavedGender(profile: unknown, gender: ProfileGender | null): Record<string, unknown> {
+  const base = profile && typeof profile === "object" && !Array.isArray(profile) ? profile as Record<string, unknown> : {};
+  return { ...base, gender };
+}