fix(telemetry): only stitch oss identities with evidence of real oss usage

MemoryClient init fired PostHog $identify for anon ids the SDKs had minted
themselves (Python: setup_config() at import time; TS: getOrCreateMem0UserId()
inside the alias path), so ~90% of stitches merged event-less anon persons
into platform users, worst in ephemeral containers.

- never create the anon id from platform client paths; Python mints lazily in
  Memory/AsyncMemory init, gated on MEM0_TELEMETRY
- record telemetry.oss_used_at when OSS Memory genuinely initializes (both
  SDKs, shared ~/.mem0/config.json key) and only stitch the oss user_id when
  the marker is present; cli anon id stays presence-based
- stamp client_version on $identify so fixed-SDK stitches are separable from
  old-SDK noise in PostHog

mem0-ts/src/client/telemetry.ts

@@ -85,6 +85,7 @@ class UnifiedTelemetry implements TelemetryClient {
       properties: {
         $anon_distinct_id: anonId,
         client_source: "typescript",
+        client_version: version,
         $lib: "posthog-node",
       },
     };