fix: preserve ingestConversation by routing through memories API

[slapglif]

Summary

• Replace ingestConversation's raw /conversations fetch (404) with an SDK-backed implementation that stores conversation transcripts via memories.add.
• Preserve the original method intent and signature while avoiding undocumented endpoints.
• Keep multi-tag behavior by storing to each provided containerTag and returning stored/partial status.

Verification

• bun run typecheck
• bun run build
• Local smoke test: ingestConversation(...) now returns success and creates memory entries.