Use Startup shortcut for Windows autostart

Replace the HKCU Run autostart entry with a per-user Startup folder shortcut. A .lnk stores TargetPath separately, which avoids fragile quoting when the executable path contains spaces.

Remove legacy PySentry and GoSentry Run entries when saving autostart settings, and report shortcut status from the actual shortcut target.

Add Windows tests that create and read a temporary shortcut with spaces in the path so the PowerShell/COM invocation remains covered.

README.md

@@ -299,12 +299,11 @@ Terminal=false
 Windows:
 
 ```text
-# PySentry writes an HKCU Run entry when Start on login is enabled. It needs no
-# administrator rights and starts PySentry when the current user signs in. Task
-# Scheduler remains a later option if delayed start or elevated tasks become
-# necessary. Saving settings with the checkbox enabled rewrites this entry, so it
-# repairs an old path after the executable was moved or renamed.
-HKCU\Software\Microsoft\Windows\CurrentVersion\Run\PySentry
+# PySentry writes a shortcut to the current user's Startup folder when Start on
+# login is enabled. A .lnk stores the executable path as a structured TargetPath,
+# so paths with spaces do not need fragile command-line quoting. Saving settings
+# rewrites the shortcut and removes old HKCU Run entries from earlier builds.
+%APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup\GoSentry.lnk
 ```
 
 ## Project Layout