Fix Intl.DateTimeFormat cross-compartment crash and Connection API robustness

OrigDateTimeFormat constructor called inside exportFunction callback failed
in Firefox compartment boundary. Moved construction to content-script-scope
helper. Also added addEventListener/removeEventListener to Connection override
to prevent crashes in real-time apps like Discord.

manifest.json

@@ -1,7 +1,7 @@
 {
   "manifest_version": 2,
   "name": "ContainSite",
-  "version": "0.5.1",
+  "version": "0.5.2",
   "description": "Per-container fingerprint isolation — each container gets its own device identity",
   "permissions": [
     "contextualIdentities",