fix: open the sign-in page instead of creating a new account on a fresh client

With no remembered account, the 2023 title screen creates a brand-new
account (grant_type create_account). On a server with sign-ups off that
fails and the title screen retries forever. PC (ClientMod) and Quest
now open the sign-in page instead, so players log into their existing
DorkNet account. AutoCreateAccount = true keeps Rec Room's behaviour.

Also replaces a literal NUL byte in the Quest config loader with '\0'.

DorkNet.Quest/dorknet-quest.cfg.example

@@ -65,6 +65,12 @@ EnableTlsTrustBypass = true
 # Accept image Content-Signatures the server signs with its own key.
 AcceptUnsignedImages = true
 
+# A headset with no remembered account. false: open the sign-in page so the
+# player logs into their existing DorkNet account. true: Rec Room's own
+# behaviour, which creates a new account automatically -- only useful when the
+# server allows sign-ups (otherwise the game keeps retrying and failing).
+AutoCreateAccount = false
+
 # ---- diagnostics (adb logcat -s DORKNET) ----
 
 LogHttp = true