fix(changes): 会话事件改走宿主 changes.ops 路由 + diff 展开二级设置 + 视觉迭代

CI 修复（plugin-mount 的 ctx.sessions.get TypeError ×1003）：
- 客户端 runtime 无事件日志面——badge/SessionLens 原在客户端直读
  ctx.sessions.get(id).events / ctx.on('session/event')，全部不可达。
- 新增宿主路由 changes.ops：live 会话日志优先，冷会话回放
  sessionPersistence.inspect；afterSeq 增量（缺省游标含 seq 0，
  显式游标为 seq > afterSeq，同 sidechat.events 约定），窗口上限
  4000 与客户端累加器一致。
- ChangesTab 轮询（mount 一拉 + visible 2.5s 增量）折入 ops，写
  模块级 opCounts 缓存供 badge 同步读取；SessionLens 改纯展示。

diff 展开二级设置（changesDiffFloat，默认浮窗）：
- prefs 四处接线 + git tab settings select（浮窗/面板，图标选项卡）
- 预览面板「展开为 diff tab」按设置落点：浮窗居中弹出或源 pane
  下方 split；i18n 全 21 词典同步。

视觉迭代（真机挂载截图审查后调整）：
- Session 视角：kind 徽章为左轨，大小+相对时间右对齐元列；失败
  操作行红色内嵌条；文件组头降为三级标签并加组间距。
- Git 视角：untracked '?' 徽章与新增同绿色；stage 按钮改 plus 图标。
- diff 折叠行：可展开折叠带 › 箭头 + 次级对比度，静态 gap 不再
  显示 pointer/hover；预览头路径改尾部截断（RTL 技巧，保文件名）。

验证：typecheck ✓ / vitest 1123 ✓ / pnpm test:mount（钉 alpha.2 CLI）
14/14 ✓；真机挂载截图（badge=5、双视角、浮窗展开）0 console error。

src/client/builtins/tabs.tsx

@@ -16,14 +16,13 @@ import { openSidebarFile } from '../intercept.tsx'
 import { EditorHost } from '../EditorHost.tsx'
 import { OpenWithSettings } from '../open-with-settings.tsx'
 import { lazyChunkComponent } from '../lazy-chunk.tsx'
-import { ChangesTab } from '../changes/ChangesTab.tsx'
-import { extractFileOps } from '../changes/ops.ts'
+import { ChangesTab, opCountOf } from '../changes/ChangesTab.tsx'
 import { DiffTab } from '../DiffTab.tsx'
 import { SubagentView } from '../SubagentView.tsx'
 import { consumeSidechatSeed, SideChatView, sidechatThreadIdOf } from '../SideChatView.tsx'
 import { api } from '../api.ts'
 import { BrowserView } from '../BrowserView.tsx'
-import { IconTerminalOutline16, IconDiffOutline16, IconGlobeOutline16 } from '../icons.tsx'
+import { IconTerminalOutline16, IconDiffOutline16, IconGlobeOutline16, IconFloatWindowOutline16, IconPanelBottomOutline16 } from '../icons.tsx'
 import { TERMINAL_FONT_SIZE_MAX, TERMINAL_FONT_SIZE_MIN } from '../../prefs-shared.ts'
 import type { ComponentType } from 'react'
 import type { SessionScope } from '../api.ts'
@@ -144,17 +143,42 @@ export function builtinTabs(ctx: Context, options: BuiltinTabOptions = {}): read
       // The unified changes tab (id kept as 'git' so persisted layouts keep
       // resolving): the Git lens is the former source-control panel; the
       // session lens is the former file-trace tab (PR #471). Both preview
-      // through one shared diff stack, and the badge counts this session's
-      // file ops (live from the event log — the git status itself needs a
-      // fetch, so it stays out of the badge).
+      // through one shared diff stack. The badge reads the op-count cache
+      // the tab's event poll publishes (the client ctx exposes no event
+      // log, and the git status needs a fetch — both stay out of the badge).
       id: 'git',
       title: () => t('changes'),
       icon: (size: number) => <IconDiffOutline16 size={size} />,
       order: 20,
       single: true,
-      badge: (ctx, scope) => {
-        const events = ctx.sessions.get(scope.sessionId)?.events
-        return events === undefined ? null : extractFileOps(events).length
+      badge: (_ctx, scope) => {
+        const count = opCountOf(scope.sessionId)
+        return count === undefined || count === 0 ? null : count
+      },
+      // Declarative settings: the diff-open picker (free window vs docked
+      // pane) renders as an iconed select row under the changes card's gear
+      // in the Side card settings page.
+      settings: {
+        toggles: [{
+          key: 'changesDiffFloat',
+          type: 'select',
+          title: () => t('changesDiffOpenTitle'),
+          desc: () => t('changesDiffOpenDesc'),
+          options: [
+            {
+              value: true,
+              icon: (size: number) => <IconFloatWindowOutline16 size={size} />,
+              title: () => t('changesDiffOpenFloat'),
+              desc: () => t('changesDiffOpenFloatDesc'),
+            },
+            {
+              value: false,
+              icon: (size: number) => <IconPanelBottomOutline16 size={size} />,
+              title: () => t('changesDiffOpenPane'),
+              desc: () => t('changesDiffOpenPaneDesc'),
+            },
+          ],
+        }],
       },
       component: ({ ctx, store, scope, tab, visible, onOpenFile, onOpenDiff }) => (
         <ChangesTab