fix: route PWD action to correct TabManager per tabId (#2147)

Previously, GHOSTTY_ACTION_PWD used AppDelegate.shared?.tabManager to
update the current working directory, which only returns the key window's
TabManager. In multi-window scenarios, cwd updates from non-key windows
were written to the wrong TabManager, causing panelDirectories to be
empty at save time and falling back to $HOME on restore.

Fix by using tabManagerFor(tabId:) to precisely route the update to
whichever window owns the tab, ensuring all windows persist their
working directories correctly.

Fixes #2125

Sources/GhosttyTerminalView.swift

@@ -2468,7 +2468,7 @@ class GhosttyApp {
                   let surfaceId = surfaceView.terminalSurface?.id else { return true }
             let pwd = action.action.pwd.pwd.flatMap { String(cString: $0) } ?? ""
             DispatchQueue.main.async {
-                AppDelegate.shared?.tabManager?.updateSurfaceDirectory(
+                AppDelegate.shared?.tabManagerFor(tabId: tabId)?.updateSurfaceDirectory(
                     tabId: tabId,
                     surfaceId: surfaceId,
                     directory: pwd