feat(workspace): 模式按钮双击收展侧栏

图标栏的「终端工作区 / SSH 工作区」按钮新增双击手势：双击当前工作区
按钮展开/收起侧栏；单击（含双击另一个按钮）只切换工作区，侧栏不动。

判定逻辑抽成零 import 纯模块 modeRailGesture.ts，用浏览器原生
MouseEvent.detail 连击计数识别手势——detail=2 到达时 store 已被
第一击更新，故在 detail=1 时把「手势前模式」存入 ref 再比对。

新增 tests/mode-rail-gesture.mjs 表驱动测试（10 例），测试数 35→36。

tests/mode-rail-gesture.mjs

@@ -0,0 +1,37 @@
+/**
+ * modeRailGesture.ts self-test。零 import 纯模块，Node 原生类型剥离直连 .ts。
+ * 锁定双击手势语义：
+ *  1) 单击 / 键盘触发（detail 1 / 0）一律 switch；
+ *  2) detail 2 只有「手势前模式 === 本按钮模式」才 toggle-sidebar（双击当前工作区按钮）；
+ *  3) detail 2 其余情况 noop（双击另一个按钮时第一击已完成切换，侧栏不动）。
+ * Run: node tests/mode-rail-gesture.mjs  (must exit 0)
+ */
+import { decideModeClick } from '../src/renderer/src/workspace/modeRailGesture.ts'
+
+let failed = 0
+const ok = (cond, msg) => {
+  console.log(`  ${cond ? 'ok' : 'FAIL'}: ${msg}`)
+  if (!cond) failed += 1
+}
+
+console.log('single click / keyboard always switch:')
+ok(decideModeClick(1, null, 'terminal') === 'switch', 'detail=1 preMode=null → switch')
+ok(decideModeClick(1, 'terminal', 'terminal') === 'switch', 'detail=1 same mode → switch')
+ok(decideModeClick(1, 'terminal', 'ssh') === 'switch', 'detail=1 other mode → switch')
+ok(decideModeClick(0, 'terminal', 'ssh') === 'switch', 'detail=0 keyboard → switch')
+
+console.log('double click toggles sidebar only on the already-active button:')
+ok(decideModeClick(2, 'terminal', 'terminal') === 'toggle-sidebar', 'detail=2 active terminal → toggle-sidebar')
+ok(decideModeClick(2, 'ssh', 'ssh') === 'toggle-sidebar', 'detail=2 active ssh → toggle-sidebar')
+ok(decideModeClick(2, 'terminal', 'ssh') === 'noop', 'detail=2 inactive ssh → noop（第一击已切换）')
+ok(decideModeClick(2, 'ssh', 'terminal') === 'noop', 'detail=2 inactive terminal → noop')
+ok(decideModeClick(2, null, 'terminal') === 'noop', 'detail=2 preMode=null → noop（防御）')
+
+console.log('click streaks beyond 2 fall back to switch semantics:')
+ok(decideModeClick(3, 'terminal', 'terminal') === 'switch', 'detail=3 → switch（不产生第二次翻转）')
+
+if (failed > 0) {
+  console.error(`${failed} check(s) failed`)
+  process.exit(1)
+}
+console.log('mode-rail-gesture: all ok')