feat(editor): 文件树「在应用中打开」子菜单（外部编辑器/图钉固定/SSH 远端/自定义编辑器） (#334)

* feat(editor): file tree 'open with' submenu (external editors, pin, SSH-remote, custom editors)

The file tree right-click menu gains an 'Open with >' submenu with the
resource manager (reveal in file manager), VS Code, Cursor and Zed, plus
user-defined custom editors (name + URL template + VSCode-family flag).
Each submenu row carries a pushpin that promotes the target to a direct
top-level menu item.

A configurable SSH host (settings: Files card gear) switches VSCode-family
openers to <scheme>://vscode-remote/ssh-remote+<host>/<path> and hides
host-local targets (file manager / Zed / non-VSCode custom editors).

External opens run through the new fenced /sidebar/api/open.external route
which spawns the platform opener with an argv array (no shell); the client
never navigates raw scheme URLs itself. The settings seam's render panel now
appends after the declarative rows instead of replacing them.

* feat(editor): polish open-with menu UI — brand icons, pushpin, chevron, row alignment

- Submenu rows: the custom label is now a block-level flex row filling the
  primitives itemLabel, so the pushpin docks at the row's far right (matching
  the trailing check of every other menu); menu row icons normalized to 16px
  (DSH native menus use 16, ours were 14).
- The submenu parent row gains a right-aligned chevron (the primitives Menu
  renders no arrow for submenu parents).
- Icons via react-icons: codicons VscPin/VscPinned pushpins (replacing the
  hand-drawn pin), VscFile/VscFolder/VscFolderOpened tree glyphs (replacing
  the </> file mark), VscLinkExternal for the open-with parent and the
  browser tab's open-external button (globally), SiCursor/SiZedindustries
  brand silhouettes; the VS Code mark is inlined from simple-icons@11.0.0
  (CC0) as IconVscode16 since later simple-icons releases dropped it. All
  monochrome currentColor to follow the active skin.
- tsdown: pin react-icons si/vsc to their ESM entries via resolve.alias —
  the package's exports map lists require before import, so the shared
  conditionNames picked the unshakeable CJS entry and bloated the core
  bundle by ~6.4 MB; tree-shaken it now adds only ~12 KB.

src/client/builtins/tabs.tsx

@@ -13,6 +13,7 @@ import { allLeaves, isAgentTabId, type SidebarState } from '../state.ts'
 import { t } from '../locales.ts'
 import { openSidebarFile } from '../intercept.tsx'
 import { EditorHost } from '../EditorHost.tsx'
+import { OpenWithSettings } from '../open-with-settings.tsx'
 import { lazyChunkComponent } from '../lazy-chunk.tsx'
 import { GitView } from '../GitView.tsx'
 import { DiffTab } from '../DiffTab.tsx'
@@ -90,7 +91,9 @@ export function builtinTabs(ctx: Context, options: BuiltinTabOptions = {}): read
       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.
+      // editor card's gear in the Side card settings page; the "open with"
+      // configuration (SSH host + custom editors) is the custom panel BELOW
+      // those rows — the settings seam renders rows first, custom panel after.
       settings: {
         toggles: [{
           key: 'editorExplorer',
@@ -112,6 +115,9 @@ export function builtinTabs(ctx: Context, options: BuiltinTabOptions = {}): read
             },
           ],
         }],
+        render: ({ pluginSettings, updatePluginSetting }) => (
+          <OpenWithSettings pluginSettings={pluginSettings} updatePluginSetting={updatePluginSetting} />
+        ),
       },
       component: ({ ctx, store, scope, tab, expanded, onToggleDir, onReferenceFile }) => (
         <EditorHost