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/TreePanel.tsx

@@ -21,6 +21,7 @@ import { IconFolderOpen16, IconRefreshOutline16 } from '@deepseek-ai/dsh-client-
 import { api } from './api.ts'
 import { FileTree } from './FileTree.tsx'
 import { IconUploadOutline16 } from './icons.tsx'
+import type { OpenWithTarget } from './open-with.ts'
 import { t } from './locales.ts'
 import { resolveSidebarPath } from './produced-files.ts'
 import { UploadOverlay } from './UploadOverlay.tsx'
@@ -50,12 +51,19 @@ export function TreePanel(props: {
   onOpenFileNewTab?: (path: string) => void
   /** File context-menu "open to the side" (passed through to FileTree). */
   onOpenFileSide?: (path: string) => void
+  /** The "open with" menu surface (passed through to FileTree; absent →
+   *  the whole section is hidden). */
+  openWithTargets?: OpenWithTarget[]
+  openWithPinned?: string[]
+  openWithSsh?: boolean
+  onOpenWith?: (targetId: string, path: string) => void
+  onToggleOpenWithPin?: (targetId: string) => void
   onReferenceFile: (path: string) => void
   /** Full-window presentation: the panel fills its host instead of docking
    *  at a fixed width. */
   full?: boolean
 }) {
-  const { sessionId, cwd, expanded, onToggle, onOpenFile, onOpenFileNewTab, onOpenFileSide, onReferenceFile, full } = props
+  const { sessionId, cwd, expanded, onToggle, onOpenFile, onOpenFileNewTab, onOpenFileSide, openWithTargets, openWithPinned, openWithSsh, onOpenWith, onToggleOpenWithPin, onReferenceFile, full } = props
   const [query, setQuery] = useState('')
   const [results, setResults] = useState<{ matches: string[]; truncated: boolean } | null>(null)
   const [error, setError] = useState<string | null>(null)
@@ -217,6 +225,11 @@ export function TreePanel(props: {
           onOpenFile={onOpenFile}
           onOpenFileNewTab={onOpenFileNewTab}
           onOpenFileSide={onOpenFileSide}
+          openWithTargets={openWithTargets}
+          openWithPinned={openWithPinned}
+          openWithSsh={openWithSsh}
+          onOpenWith={onOpenWith}
+          onToggleOpenWithPin={onToggleOpenWithPin}
           onReferenceFile={onReferenceFile}
           refreshTick={refreshTick}
           onUploadRequest={startUpload}