fix(updater): installer waits for the old cinny.exe to release (#1)

The updater launches the NSIS installer with /UPDATE and then exits the
app, but a WebView2 app takes a moment to die and the template only
sleeps 500 ms after its own kill before copying — so the copy raced the
old process ("Error opening file for writing: cinny.exe"), and Ignore
left the old exe in place.

A NSIS_HOOK_PREINSTALL now, on /UPDATE only, polls until cinny.exe can
really be opened for writing (every 250 ms, up to 15 s), then lets the
template carry on. Checked under Wine with a real running exe: without
the hook the copy fails; with it the installer waits out the remaining
~2.8 s and copies; a manual install (no /UPDATE) doesn't wait; a stuck
process hits the 15 s cap and falls through to the template's own
running-app handling.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src-tauri/tauri.conf.json

@@ -10,7 +10,8 @@
         "type": "downloadBootstrapper"
       },
       "nsis": {
-        "installMode": "currentUser"
+        "installMode": "currentUser",
+        "installerHooks": "./nsis/hooks.nsh"
       },
       "wix": {
         "bannerPath": "wix/banner.bmp",