fix(analytics): declare the script build arg and send the Track API's real envelope

Two blockers found while wiring OpenPanel for real:

- frontend/Dockerfile declared ARG for VITE_OPENPANEL_URL/CLIENT_ID/SENTRY_DSN but not
  VITE_OPENPANEL_SCRIPT_URL, so passing it as a build arg was silently ignored and the
  loader compiled out (import.meta.env value undefined).
- backend/app/services/analytics.py posted a flat {type, event, properties} body; the
  Track API expects {type, payload:{event, properties, profileId}} (verified against the
  SDK source in packages/sdks/sdk). The API answered 400 and the module swallows every
  error by design, so all server-side events were being dropped without a trace.

Verified after deploy: the bundle carries the client id + op1.js URL + the queueing shim,
op1.js serves 200, and a track event posted with the real envelope lands in OpenPanel.

backend/app/services/analytics.py

@@ -37,13 +37,12 @@ async def track(event: str, properties: dict[str, Any] | None = None, profile_id
     """Record a named event; swallows every error."""
     if not _configured():
         return
-    body = {
-        "type": "track",
-        "event": event,
-        "properties": properties or {},
-    }
+    # OpenPanel's Track API takes {type, payload:{…}} (same envelope the browser SDK
+    # sends) — a flat body is rejected with 400, which this module swallows by design.
+    inner: dict[str, Any] = {"event": event, "properties": properties or {}}
     if profile_id:
-        body["profileId"] = profile_id
+        inner["profileId"] = profile_id
+    body = {"type": "track", "payload": inner}
     try:
         async with httpx.AsyncClient(timeout=_TIMEOUT) as client:
             await client.post(
@@ -66,7 +65,7 @@ async def identify(profile_id: str, properties: dict[str, Any] | None = None) ->
         async with httpx.AsyncClient(timeout=_TIMEOUT) as client:
             await client.post(
                 f"{settings.OPENPANEL_API_URL.rstrip('/')}/track",
-                json={"type": "identify", "profileId": profile_id, "properties": properties or {}},
+                json={"type": "identify", "payload": {"profileId": profile_id, "properties": properties or {}}},
                 headers={
                     "openpanel-client-id": settings.OPENPANEL_CLIENT_ID,
                     "openpanel-client-secret": settings.OPENPANEL_CLIENT_SECRET,