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/prefs-shared.ts

@@ -60,6 +60,15 @@ export interface SidebarPrefs {
    * own enable switch gates it too (both must be on for the takeover).
    */
   interceptOpenPath: boolean
+  /**
+   * Whether the editor tab runs in merged mode: a path input replaces the
+   * plain header and a toggleable file-tree panel (with a global name
+   * search) docks at the tab's right edge. On by default; also makes brand
+   * new sessions seed an empty editor tab (tree panel open) instead of the
+   * explorer tab. The switch lives under the editor card's gear in the
+   * Side card settings; off restores the pre-merge editor exactly.
+   */
+  editorExplorer: boolean
   /**
    * Position compatibility mode: reserves space at the top for the native
    * Windows title bar (drawn at the window's top-right corner over the web
@@ -156,7 +165,7 @@ export interface SidebarPrefs {
 /** Range contract of {@link SidebarPrefs.defaultWidthPercent}. */
 export const WIDTH_PERCENT_MIN = 20
 export const WIDTH_PERCENT_MAX = 60
-export const WIDTH_PERCENT_DEFAULT = 30
+export const WIDTH_PERCENT_DEFAULT = 35
 
 /** Range contract of {@link SidebarPrefs.terminalFontSize}. */
 export const TERMINAL_FONT_SIZE_MIN = 9
@@ -170,7 +179,7 @@ export const TITLE_BAR_STRIP_DEFAULT = 40
 
 /** Fallback prefs used whenever the settings document is unreachable or malformed. */
 export const SIDEBAR_PREFS_DEFAULTS: SidebarPrefs = {
-  openByDefault: true,
+  openByDefault: false,
   defaultWidthPercent: WIDTH_PERCENT_DEFAULT,
   autoOpenSubagent: true,
   autoOpenJobs: true,
@@ -179,6 +188,7 @@ export const SIDEBAR_PREFS_DEFAULTS: SidebarPrefs = {
   terminalFontFamily: '',
   terminalFontSize: TERMINAL_FONT_SIZE_DEFAULT,
   interceptOpenPath: true,
+  editorExplorer: true,
   titleBarCompat: false,
   titleBarStripPx: TITLE_BAR_STRIP_DEFAULT,
   htmlViewerNoSandbox: false,