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/SideCardSection.module.css

@@ -403,6 +403,59 @@
   width: 76px;
 }
 
+/* Select rows: the closed anchor is a compact button (selected option's
+   icon when the options carry icons, plus title and a chevron); the dropdown
+   itself is the primitives Menu (portal). */
+.selectAnchor {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  max-width: 220px;
+  padding: 4px 8px;
+  border: 1px solid var(--dsw-alias-border-l2);
+  border-radius: 8px;
+  background: var(--dsw-alias-bg-layer-3);
+  color: var(--dsw-alias-label-primary);
+  font-size: 13px;
+  line-height: 20px;
+  cursor: pointer;
+}
+
+.selectAnchor:hover {
+  border-color: var(--dsw-alias-label-dimmed);
+}
+
+.selectAnchorIcon {
+  display: inline-flex;
+  flex: none;
+}
+
+.selectAnchorText {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+/* One big-icon option card inside the select dropdown. */
+.selectOption {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  min-width: 200px;
+}
+
+.selectOptionIcon {
+  display: inline-flex;
+  flex: none;
+  color: var(--dsw-alias-label-secondary);
+}
+
+.selectOptionText {
+  display: flex;
+  flex-direction: column;
+  min-width: 0;
+}
+
 .suffix {
   font-size: 14px;
   line-height: 22px;