feat(editor): 文件窗口与资源管理器二合一 + 声明式设置 select 行 (#151)

* feat(editor): merged explorer mode — path input, docked file tree, global name search

New editorExplorer pref (default on, editor card gear): the editor tab gains
a path-input header and a toggleable right-docked tree panel (per-tab state
in tab.meta.treeOpen; file tabs default closed, the seeded path-less home
tab defaults open). Fresh sessions seed that empty editor tab instead of
the explorer tab when merged mode is on; the standalone explorer tab stays
in the + menu unchanged.

- Extract FileTree.tsx from ExplorerView (shared by both hosts)
- Host fs.search route: recursive case-insensitive name search rooted at
  the session cwd, budget-capped (200 matches / 100k visited), skips .git,
  never descends symlink dirs
- EditorHost reads the pref reactively (boolean snapshot) and keeps the
  pre-merge layout verbatim when off

* feat(settings): select row type for declarative settings; editorExplorer as iconed select

- SidebarSettingToggle gains type 'select' with options {value,title,desc,icon}
  and multi (default false; stores the picked values as an array in options
  order). Any option carrying an icon renders big-icon option cards in the
  dropdown and the icon in the closed anchor; icon-less rows are one-line text.
- SelectRow in SideCardSection rides the primitives Menu (portal); single-pick
  commits and closes, multi toggles and stays open. Wired for both host-prefs
  toggles and plugin-owned pluginToggles via the new onSelectValue seam.
- The editorExplorer merged-mode pref is now an iconed select (merged vs
  separate) instead of a switch; the stored value stays boolean.
- Advertise the capability as 'settingSelect' in SIDEBAR_FEATURES.

* feat(editor): unify explorer into the editor surface, resizable tree dock, hoisted toolbar

- One tree implementation, two presentations: the shared TreePanel (global
  name search + refresh + FileTree) docks as the editor tab's right panel
  and — in merged mode — fills the explorer tab's window; the pref-off
  explorer keeps its legacy header shell.
- The docked panel drag-resizes from its left edge (160-480px clamp),
  persisted as tab.meta.treeWidth alongside treeOpen.
- The text editor's preview/edit/save toolbar moves into the path-input
  header row: FileViewerProps gains internal toolbar fields ('host' mode
  skips the viewer's own row, reports EditorToolbarState and registers
  EditorToolbarControls); non-merged mode is byte-identical to before.

* feat(editor): single files window with in-place switching; explorer descriptor removed

- editor tab replaces explorer on the + menu (order 10, Files); persisted
  explorer tabs migrate to the editor home tab via sanitizeState
- editorExplorer now only controls open behavior: merged = in-place
  updateTab, independent = openSidebarFile; both modes share the merged
  chrome (path input + hoisted preview/edit/save toolbar + tree toggle)
- file tree context menu gains 'open in new tab' / 'open to the side'
  (mintTabId avoids the id safety net; insertLeafAt splits right)
- tree dock resize uses pointer capture (touch-action none, 6px handle)
- defaults: openByDefault off, sidebar width 35%
- file tree clips horizontal overflow (no sideways scroll)
- e2e: mount lane arms the editor-chunk wait before goto and clicks the
  tree row's left edge (hover @-reference button sits mid-row); drag lane
  expands the panel first (collapsed push writes 0px), waits for the
  slide-in to settle, and picks the leftmost col-resize strip; 'Files'
  title assertions require draggable to skip the bottom panel's welcome
  cards

* feat(editor): split mode turns the path-less window into the standalone explorer

In independent (split) mode a path-less files window renders ONLY the
tree panel (search + FileTree, full-window form) — no path input, no
hoisted toolbar, no tree toggle. File clicks open per-path editor tabs
(full chrome, tree docked closed by default) through openSidebarFile,
unchanged. Merged mode is untouched (chrome + docked tree, in-place
switching). TreePanel's previously reserved 'full' prop now has its
consumer.

src/client/builtins/tabs.tsx

@@ -1,17 +1,17 @@
 /**
- * The 7 built-in tab descriptors: the plugin registers its own pages
- * (explorer / git / terminal / browser / subagent / editor / diff) through
+ * The 6 built-in tab descriptors: the plugin registers its own pages
+ * (editor / git / terminal / browser / subagent / diff) through
  * the same {@link BetterSidebarService} external plugins use — eating its
  * own dogfood. The terminal descriptor owns its quota (`TERMINAL_LIMIT`)
  * and mints `terminal:<n>` ids through `createTab`; the browser mints
- * `browser:<n>` the same way (no quota).
+ * `browser:<n>` the same way (no quota). The editor IS the files window
+ * (the old standalone explorer merged into it).
  */
-import { IconBranchOutline16, IconCodeOutline16, IconFolderOpen16, IconThinkOutline16 } from '@deepseek-ai/dsh-client-ui-primitives'
+import { IconBranchOutline16, IconCodeOutline16, IconFolderOpen16, IconPanelLeftOutline16, IconThinkOutline16 } from '@deepseek-ai/dsh-client-ui-primitives'
 import type { Context } from '../../context-types.ts'
 import { allLeaves, isAgentTabId, type SidebarState } from '../state.ts'
 import { t } from '../locales.ts'
 import { openSidebarFile } from '../intercept.tsx'
-import { ExplorerView } from '../ExplorerView.tsx'
 import { EditorHost } from '../EditorHost.tsx'
 import { lazyChunkComponent } from '../lazy-chunk.tsx'
 import { GitView } from '../GitView.tsx'
@@ -59,33 +59,52 @@ function uiTerminalCount(state: SidebarState): number {
     .filter(tab => tab.type === 'terminal' && !isAgentTabId(tab.id)).length
 }
 
-/** The 7 built-in tab descriptors. */
+/** The 6 built-in tab descriptors. */
 export function builtinTabs(ctx: Context): readonly TabDescriptor[] {
   return [
     {
       id: 'editor',
-      title: () => t('editor'),
-      icon: (size: number) => <IconCodeOutline16 size={size} />,
-      order: -1,
-      hidden: true,
-      dedupeKey: (tab) => tab.path,
-      component: ({ ctx, store, scope, tab }) => (
-        <EditorHost ctx={ctx} store={store} scope={scope} path={tab.path ?? ''} title={tab.title} />
-      ),
-    },
-    {
-      id: 'explorer',
-      title: () => t('explorer'),
+      // The single files window: an editor tab with no path IS the file
+      // explorer (empty hint + docked tree); with a path it previews/edits
+      // the file. Visible in the + menu in the explorer's old slot.
+      title: () => t('files'),
       icon: (size: number) => <IconFolderOpen16 size={size} />,
       order: 10,
-      single: true,
-      component: ({ ctx, store, scope, expanded, onToggleDir, onReferenceFile }) => (
-        <ExplorerView
-          sessionId={scope.sessionId}
-          cwd={scope.cwd}
+      hidden: false,
+      dedupeKey: (tab) => tab.path,
+      // Declarative settings: the file-open behavior picker (in-place switch
+      // vs per-path windows) renders as an iconed select row under the
+      // editor card's gear in the Side card settings page.
+      settings: {
+        toggles: [{
+          key: 'editorExplorer',
+          type: 'select',
+          title: () => t('editorExplorer'),
+          desc: () => t('editorExplorerDesc'),
+          options: [
+            {
+              value: true,
+              icon: (size: number) => <IconPanelLeftOutline16 size={size} />,
+              title: () => t('editorExplorerMerged'),
+              desc: () => t('editorExplorerMergedDesc'),
+            },
+            {
+              value: false,
+              icon: (size: number) => <IconCodeOutline16 size={size} />,
+              title: () => t('editorExplorerSplit'),
+              desc: () => t('editorExplorerSplitDesc'),
+            },
+          ],
+        }],
+      },
+      component: ({ ctx, store, scope, tab, expanded, onToggleDir, onReferenceFile }) => (
+        <EditorHost
+          ctx={ctx}
+          store={store}
+          scope={scope}
+          tab={tab}
           expanded={expanded ?? []}
-          onToggle={onToggleDir ?? (() => { /* no-op */ })}
-          onOpenFile={(path) => { openSidebarFile(ctx, store, scope.sessionId, path) }}
+          onToggleDir={onToggleDir ?? (() => { /* no-op */ })}
           onReferenceFile={onReferenceFile ?? (() => { /* no-op */ })}
         />
       ),