UI 修复: 回复页（ReplyBar）加往返预算配置入口

jianf 反馈：回复页面/对话页面/发件页面无法配置对话预算。
- 发件页（ComposePage）：已有 maxRounds 输入框 ✅
- 对话页（MailView 会话头部）：已有 BudgetEditor ✅
- 回复页（ReplyBar）：缺失 ← 本轮补上

ReplyBar 底部按钮区加预算徽标（点击展开编辑）：
- 显示 已用/上限 来回 或「预算不限」，用尽时红色
- 点击 → 数字输入 + 保存/取消
- 复用 useSessionStore.setBudget（同一会话）
- 177 测试全过，已部署

web/src/components/MailView.tsx

@@ -676,6 +676,9 @@ function ReplyBar({
   // 抄送默认收起：多数回复不需要它，常驻一行输入框只会挤掉正文空间。
   // 原邮件带抄送时自动展开并预填 —— 「回复全部」是人在这种场景下的默认预期
   const [ccOpen, setCcOpen] = useState(false);
+  const [budgetEditing, setBudgetEditing] = useState(false);
+  const [budgetBusy, setBudgetBusy] = useState(false);
+  const [maxRoundsDraft, setMaxRoundsDraft] = useState('');
   const [attachments, setAttachments] = useState<PendingAttachment[]>([]);
   const [busy, setBusy] = useState(false);
   const [error, setError] = useState<string | null>(null);
@@ -684,6 +687,8 @@ function ReplyBar({
   const fetchSessions = useSessionStore(s => s.fetchSessions);
   const fetchContacts = useContactStore(s => s.fetchContacts);
   const selectSession = useSessionStore(s => s.selectSession);
+  const budget = useSessionStore(s => s.budget);
+  const setBudget = useSessionStore(s => s.setBudget);
   const me = useAuthStore(s => s.user?.username || '');
 
   if (!replyTo) return null;
@@ -774,6 +779,58 @@ function ReplyBar({
       <div className="flex items-center gap-2 mt-2 flex-wrap">
         {error && <span className="text-xs text-red-600 min-w-0 break-words">{error}</span>}
         <div className="flex-1" />
+        {budget && !budgetEditing && (
+          <button
+            onClick={() => {
+              setMaxRoundsDraft(budget.unlimited ? '' : String(budget.max_rounds));
+              setBudgetEditing(true);
+            }}
+            title="本任务往返预算：Agent 主动发信上限（自动转发与权限询问不占）"
+            className={`tap inline-flex items-center gap-1 text-[10px] px-2 py-1 rounded border ${
+              budget.unlimited
+                ? 'border-gray-200 text-gray-500 hover:border-blue-300'
+                : budget.remaining === 0
+                  ? 'border-red-200 text-red-600'
+                  : 'border-gray-200 text-gray-500 hover:border-blue-300'
+            }`}
+          >
+            <GaugeIcon className="w-3 h-3" />
+            {budget.unlimited
+              ? '预算不限'
+              : `${budget.used_rounds}/${budget.max_rounds} 来回${budget.remaining === 0 ? ' · 已用尽' : ''}`}
+          </button>
+        )}
+        {budget && budgetEditing && (
+          <span className="inline-flex items-center gap-1">
+            <span className="text-[10px] text-gray-500">预算</span>
+            <input
+              value={maxRoundsDraft}
+              onChange={e => setMaxRoundsDraft(e.target.value)}
+              inputMode="numeric"
+              placeholder="不限"
+              autoFocus
+              className="w-14 text-xs border border-gray-300 rounded px-1.5 py-0.5 focus:outline-none focus:ring-2 focus:ring-blue-100"
+            />
+            <button
+              disabled={budgetBusy || (maxRoundsDraft.trim() !== '' && !/^\d+$/.test(maxRoundsDraft.trim()))}
+              onClick={async () => {
+                setBudgetBusy(true);
+                await setBudget({ max_rounds: maxRoundsDraft.trim() === '' ? 0 : Number(maxRoundsDraft.trim()) });
+                setBudgetBusy(false);
+                setBudgetEditing(false);
+              }}
+              className="tap px-2 py-0.5 text-[10px] rounded bg-blue-600 text-white hover:bg-blue-700 disabled:opacity-40"
+            >
+              保存
+            </button>
+            <button
+              onClick={() => setBudgetEditing(false)}
+              className="tap text-[10px] text-gray-400 hover:text-gray-700"
+            >
+              ×
+            </button>
+          </span>
+        )}
         <button
           onClick={() => {
             setBody('');