fix: v2.5.3 — Windows workspace folders, picker on top, no console flashes

A workspace could not be created on Windows: "cwd must be an absolute path"
for D:\…, because createLane/canonicalCwd tested for a leading "/".

- lanes.js: path.isAbsolute/path.resolve; canonicalCwd stops at any root (a
  missing drive looped forever); resolveLaneByCwd and /ensure accept "\" too
- native-dialog.js: the Windows picker gets an invisible TopMost owner form,
  shown first — an ownerless dialog from the background server opened behind
  the browser, or hidden
- windows-hide.js: every child process on Windows starts with windowsHide,
  required first by the server and the detached scripts (a console window
  flashed per git/npm call)
- Confirm/update/clear-data modals and the quota panel scroll instead of
  overflowing a short window

client/src/components/ConfirmModal.tsx

@@ -85,14 +85,14 @@ export function ConfirmModal({
     >
       <div
         ref={panelRef}
-        className="relative w-full max-w-md rounded-xl border border-border bg-surface-1 shadow-xl shadow-black/40"
+        className="relative flex max-h-full w-full max-w-md flex-col rounded-xl border border-border bg-surface-1 shadow-xl shadow-black/40"
         onClick={(e) => e.stopPropagation()}
         role="dialog"
         aria-modal="true"
         aria-labelledby={titleId}
         aria-describedby={message ? messageId : undefined}
       >
-        <div className="flex items-start gap-3 p-5">
+        <div className="flex min-h-0 items-start gap-3 overflow-y-auto p-5">
           {destructive && (
             <div className="w-9 h-9 rounded-lg bg-status-danger/10 border border-status-danger/20 flex items-center justify-center flex-shrink-0">
               <AlertTriangle className="w-4.5 h-4.5 text-status-danger" aria-hidden />