Add Supabase semantic recall layer

[splinesreticulating]

Summary

• add Supabase and OpenAI clients plus a pgvector-backed message_embeddings table and RPC for similarity search
• index freshly fetched iMessages into Supabase using OpenAI text embeddings and surface top-k similar snippets in the reply context
• expand tests to cover the new indexing metadata and context augmentation logic

Testing

• yarn test

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https://chatgpt.com/codex/tasks/task_e_68d87e17fe2883209ce3c3a4925937dc