feat(autostart): suppress browser auto-open on Windows login

When the user enables "Start with Windows" in the installer, the app
launches on every PC login. Previously each login popped a fresh WebUI
tab, which is noisy for a tray-resident background service.

The autostart shortcut now passes --autostart to start-hidden.vbs, which
sets LEDGRAB_AUTOSTART=1 in the child env. __main__ checks this flag
alongside LEDGRAB_RESTART when deciding whether to open the browser.

Manual launches (desktop/start-menu shortcuts) and the installer's
post-install "Launch LedGrab" finish-page action are unchanged — they
don't pass the arg, so they still open the WebUI tab.

server/scripts/start-hidden.vbs

@@ -10,6 +10,15 @@ Set procEnv = WshShell.Environment("Process")
 procEnv("PYTHONPATH") = appRoot & "\app\src"
 procEnv("LEDGRAB_CONFIG_PATH") = appRoot & "\app\config\default_config.yaml"
 
+' If launched as Windows autostart (via the SMSTARTUP shortcut), suppress the
+' browser auto-open. Manual launches (desktop / start menu) pass no args.
+For Each arg In WScript.Arguments
+    If arg = "--autostart" Then
+        procEnv("LEDGRAB_AUTOSTART") = "1"
+        Exit For
+    End If
+Next
+
 ' Use embedded python.exe (NOT pythonw.exe) with WindowStyle=0.
 ' Same pattern as the Media Server sibling app.
 embeddedPython = appRoot & "\python\python.exe"