Use lunar calendar input for birth date with solar conversion display.

Add LunarBirthPicker for bazi and combined forms, converting lunar input to solar for chart calculation.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/calc/lunar-date.ts

@@ -0,0 +1,79 @@
+import { Lunar, Solar } from "lunar-javascript";
+
+export interface LunarDateParts {
+  year: number;
+  month: number;
+  day: number;
+  isLeapMonth: boolean;
+}
+
+/** 农历 → 阳历 YYYY-MM-DD，无效则 null */
+export function lunarToSolarYmd(parts: LunarDateParts): string | null {
+  try {
+    const month = parts.isLeapMonth ? -parts.month : parts.month;
+    const lunar = Lunar.fromYmd(parts.year, month, parts.day);
+    return lunar.getSolar().toYmd();
+  } catch {
+    return null;
+  }
+}
+
+/** 阳历 YYYY-MM-DD → 农历分量 */
+export function solarYmdToLunarParts(ymd: string): LunarDateParts | null {
+  try {
+    const [y, m, d] = ymd.split("-").map(Number);
+    if (!y || !m || !d) {
+      return null;
+    }
+    const lunar = Solar.fromYmd(y, m, d).getLunar();
+    const month = lunar.getMonth();
+    return {
+      year: lunar.getYear(),
+      month: Math.abs(month),
+      day: lunar.getDay(),
+      isLeapMonth: month < 0,
+    };
+  } catch {
+    return null;
+  }
+}
+
+/** 格式化农历显示 */
+export function formatLunarLabel(parts: LunarDateParts): string | null {
+  try {
+    const month = parts.isLeapMonth ? -parts.month : parts.month;
+    return Lunar.fromYmd(parts.year, month, parts.day).toString();
+  } catch {
+    return null;
+  }
+}
+
+/** 格式化阳历显示 */
+export function formatSolarLabel(ymd: string): string | null {
+  try {
+    const [y, m, d] = ymd.split("-").map(Number);
+    if (!y || !m || !d) {
+      return null;
+    }
+    const solar = Solar.fromYmd(y, m, d);
+    const week = ["日", "一", "二", "三", "四", "五", "六"][solar.getWeek()];
+    return `${y}年${m}月${d}日 星期${week}`;
+  } catch {
+    return null;
+  }
+}
+
+export function todayLunarParts(): LunarDateParts {
+  const lunar = Solar.fromDate(new Date()).getLunar();
+  const month = lunar.getMonth();
+  return {
+    year: lunar.getYear(),
+    month: Math.abs(month),
+    day: lunar.getDay(),
+    isLeapMonth: month < 0,
+  };
+}
+
+export function todaySolarYmd(): string {
+  return Solar.fromDate(new Date()).toYmd();
+}