refactor(mem0-agent): stop requiring org/project in client config

An API key is already bound to one (org_id, project_id) server-side, so storing a
copy locally was redundant state that can go stale. Verified live that add,
get_all and feedback all succeed with no ids in the body at all.

- both ids are now purely an OVERRIDE, for pointing one key at a different
  project in the same org; half an override is ignored rather than half-applied
- identity resolution no longer persists scope as a side effect
- the project-config endpoints (the only ones needing ids in the URL) resolve
  them from /v1/ping/ and cache the result
- corrects an over-generalized finding: feedback does not require the ids; it
  404'd earlier only because that memory lived outside the key's project
- onboarding now recommends a key issued for a dedicated project over an override

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

integrations/mem0-agent/src/mem0_agent/settings.py

@@ -134,11 +134,9 @@ def resolve_user_id(api, settings: Settings | None = None) -> str:
         email = body.get("user_email") or ""
         uid = email.split("@")[0] if email else ""
         if uid:
+            # Cache the identity only. Scope is deliberately NOT persisted: the API key
+            # already carries it, and storing a copy here would be state that can go stale.
             settings.set("user_id", uid)
-            if body.get("org_id"):
-                settings.set("org_id", body["org_id"])
-            if body.get("project_id"):
-                settings.set("default_project_id", body["project_id"])
             return uid
     return os.environ.get("USER", "default")