feat(posts): 类型帖截止时间、抽奖奖品表与悬赏发帖体验

统一投票/悬赏/抽奖截止与状态展示，抽奖支持多奖品行；发帖页悬赏积分对齐表格输入，并在余额不足时于底部就地提示。

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

frontend/components/DeadlinePicker.tsx

@@ -0,0 +1,130 @@
+"use client";
+
+/** 发帖截止时间：快捷天数 + 自定义时刻 */
+
+export type DeadlineMode = "preset" | "custom";
+
+function pad2(n: number) {
+  return String(n).padStart(2, "0");
+}
+
+/** datetime-local 值（本地时区） */
+export function toLocalInputValue(d: Date): string {
+  return `${d.getFullYear()}-${pad2(d.getMonth() + 1)}-${pad2(d.getDate())}T${pad2(d.getHours())}:${pad2(d.getMinutes())}`;
+}
+
+/** 默认自定义：从现在起 +N 天 */
+export function defaultCustomLocal(days = 7): string {
+  const d = new Date();
+  d.setDate(d.getDate() + days);
+  d.setSeconds(0, 0);
+  return toLocalInputValue(d);
+}
+
+/** 本地 datetime-local → RFC3339（UTC） */
+export function localInputToRFC3339(local: string): string | null {
+  const t = Date.parse(local);
+  if (!Number.isFinite(t)) return null;
+  return new Date(t).toISOString().replace(/\.\d{3}Z$/, "Z");
+}
+
+export function formatLocalPreview(local: string): string {
+  const t = Date.parse(local);
+  if (!Number.isFinite(t)) return "";
+  try {
+    return new Date(t).toLocaleString("zh-CN");
+  } catch {
+    return local;
+  }
+}
+
+export default function DeadlinePicker({
+  label = "截止时间",
+  presets,
+  mode,
+  onModeChange,
+  days,
+  onDaysChange,
+  customLocal,
+  onCustomLocalChange,
+  disabled,
+  hint,
+}: {
+  label?: string;
+  presets: readonly number[];
+  mode: DeadlineMode;
+  onModeChange: (m: DeadlineMode) => void;
+  days: number;
+  onDaysChange: (d: number) => void;
+  customLocal: string;
+  onCustomLocalChange: (v: string) => void;
+  disabled?: boolean;
+  hint?: string;
+}) {
+  const minLocal = toLocalInputValue(new Date(Date.now() + 60 * 60 * 1000));
+  const maxLocal = toLocalInputValue(new Date(Date.now() + 90 * 24 * 60 * 60 * 1000));
+
+  return (
+    <div className="j13-deadline-picker">
+      <div className="j13-deadline-picker-label">{label}</div>
+      <div className="j13-deadline-picker-modes" role="tablist" aria-label={label}>
+        <button
+          type="button"
+          role="tab"
+          aria-selected={mode === "preset"}
+          className={`j13-deadline-mode${mode === "preset" ? " is-on" : ""}`}
+          disabled={disabled}
+          onClick={() => onModeChange("preset")}
+        >
+          快捷时长
+        </button>
+        <button
+          type="button"
+          role="tab"
+          aria-selected={mode === "custom"}
+          className={`j13-deadline-mode${mode === "custom" ? " is-on" : ""}`}
+          disabled={disabled}
+          onClick={() => {
+            onModeChange("custom");
+            if (!customLocal) onCustomLocalChange(defaultCustomLocal(days || 7));
+          }}
+        >
+          指定时刻
+        </button>
+      </div>
+
+      {mode === "preset" ? (
+        <div className="j13-deadline-presets">
+          {presets.map((d) => (
+            <button
+              key={d}
+              type="button"
+              className={`btn btn-sm ${days === d ? "btn-primary" : "btn-line"}`}
+              disabled={disabled}
+              onClick={() => onDaysChange(d)}
+            >
+              {d} 天
+            </button>
+          ))}
+        </div>
+      ) : (
+        <div className="j13-deadline-custom">
+          <input
+            type="datetime-local"
+            className="j13-compose-field j13-deadline-datetime"
+            value={customLocal}
+            min={minLocal}
+            max={maxLocal}
+            disabled={disabled}
+            onChange={(e) => onCustomLocalChange(e.target.value)}
+            aria-label="指定截止时刻"
+          />
+          {customLocal ? (
+            <p className="meta text-[12.5px] !mb-0">将于 {formatLocalPreview(customLocal)} 截止</p>
+          ) : null}
+        </div>
+      )}
+      {hint ? <p className="meta text-[12px] !mb-0">{hint}</p> : null}
+    </div>
+  );
+}