feat: 编排器跨项目全局并发上限闸（tsk_erQHNYdn6i9g）

新增用户级设置项 globalConcurrency（settings 表，独立于新建项目默认值
来源 concurrency），缺省 0 = 不限，向后兼容无需 DB 迁移。

- store: UserSettings 加 globalConcurrency 字段 + 默认 0；新增
  globalInflightCount()（跨所有项目 started run 总数，与 inflightTaskIds 同口径）
- orchestrator.claimTick: 叠加全局闸，与 per-project 闸串联（都过才领）；
  轮初查一次全局在途、轮内手动 ++，达上限即 return 跨所有项目停止领取
- api: PUT /api/settings 支持 globalConcurrency（空/null 归一为 0）
- web: 侧栏「全局设置」入口 + 模态，编辑/回显/校验（≥0 整数）
- test: 新增全局闸达上限跨项目阻止 / 未达上限正常领取 / 边界 / 轮初短路 用例

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/app.js

@@ -132,6 +132,10 @@ const I18N = {
     toastNameRequired: '名称与仓库路径必填',
     toastTaskNotFound: '任务不在当前项目',
     toastConcInt: '最大并发必须是 ≥1 的整数',
+    globalSettings: '全局设置', globalConc: '全局并发上限',
+    globalConcHint: '跨所有项目的在途任务总数上限；0 = 不限。',
+    globalConcInt: '全局并发上限必须是 ≥0 的整数（0 = 不限）',
+    toastSettingsSaved: '全局设置已保存',
     toastRejectRequired: '驳回意见不能为空',
     reorderSaved: '项目顺序已保存',
     cancelConfirm: '确定取消任务「{title}」{hint}？\n取消后任务进入归档，不影响子任务执行。',
@@ -274,6 +278,10 @@ const I18N = {
     toastNameRequired: 'Name and repo path are required',
     toastTaskNotFound: 'Task not found in current project',
     toastConcInt: 'Max concurrency must be an integer ≥1',
+    globalSettings: 'Settings', globalConc: 'Global concurrency cap',
+    globalConcHint: 'Max in-flight tasks across all projects; 0 = unlimited.',
+    globalConcInt: 'Global concurrency cap must be an integer ≥0 (0 = unlimited)',
+    toastSettingsSaved: 'Settings saved',
     toastRejectRequired: 'Rejection feedback is required',
     reorderSaved: 'Project order saved',
     cancelConfirm: 'Cancel task "{title}"{hint}?\nThis moves the task to archive; subtasks are unaffected.',
@@ -1752,6 +1760,17 @@ document.addEventListener('click', (ev) => {
       $('#modalRoot').hidden = true;
       break;
 
+    case 'open-settings':
+      api('/api/settings').then((s) => {
+        $('#setGlobalConc').value = s.globalConcurrency ?? 0;
+        $('#settingsRoot').hidden = false;
+        $('#setGlobalConc').focus();
+      }).catch((e) => toast(e.message));
+      break;
+    case 'close-settings':
+      $('#settingsRoot').hidden = true;
+      break;
+
     case 'toggle-new-task': {
       const p = $('#newTaskPanel');
       p.hidden = !p.hidden;
@@ -2234,6 +2253,16 @@ $('#newProjectForm').addEventListener('submit', (ev) => {
   }, t('toastProjectCreated', { name }));
 });
 
+$('#settingsForm').addEventListener('submit', (ev) => {
+  ev.preventDefault();
+  const n = Number($('#setGlobalConc').value);
+  if (!Number.isInteger(n) || n < 0) { toast(t('globalConcInt')); return; }
+  act(async () => {
+    await api('/api/settings', { method: 'PUT', body: JSON.stringify({ globalConcurrency: n }) });
+    $('#settingsRoot').hidden = true;
+  }, t('toastSettingsSaved'));
+});
+
 $('#newTaskPanel').addEventListener('submit', (ev) => {
   ev.preventDefault();
   const f = ev.target;
@@ -2268,6 +2297,7 @@ document.addEventListener('keydown', (ev) => {
     const am = $('#archiveModalRoot');
     if (!am.hidden) { am.hidden = true; am.innerHTML = ''; return; }
     if (S.previewId) { S.previewId = null; S.previewReject = false; renderPreview(); return; }
+    if (!$('#settingsRoot').hidden) { $('#settingsRoot').hidden = true; return; }
     $('#modalRoot').hidden = true;
   }
 });