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

server/routes/lanes.js

@@ -406,7 +406,7 @@ router.post("/ensure", sameOriginGuard, (req, res) => {
   // it, a nested cwd still resolves to its owner, which is what the CLI and
   // other callers adopting "the lane I am inside" rely on.
   const found = lanesLib.resolveLaneByCwd(cwd, body.tool || "claude");
-  const strip = (p) => p.replace(/\/+$/, "");
+  const strip = (p) => p.replace(/[\\/]+$/, "");
   const owner = found && (body.exact !== true || strip(found.cwd) === strip(cwd)) ? found : null;
   if (owner) {
     // First-write wins on the title: an ensure-with-title on an existing lane