Add supabase_direct storage backend

[pavanputhra]

Summary

• New server/storage/supabase_direct/ module: writes vCon directly to a Supabase Postgres schema (vcons + parties + dialog + analysis + attachments) via a long-lived psycopg2 connection per worker process, with multi-row INSERTs per vCon.
• Bypasses the vcon-mcp HTTP layer entirely.
• Retries forever on connection / query failures rather than DLQing — intended for deployments where Postgres is colocated and brief outages should be absorbed transparently.

Authorship

Code authored by @howejacob1 — opening on his behalf so review can start. He can take over the branch or push fixups directly.

Open questions for review

• Should the "retry forever, never DLQ" choice be the default, or gated behind an option?
• Worth a quick sanity check on the schema mapping vs. the canonical vcon-mcp writes, in case fields drift over time.

Test plan

• Configure a chain to use this backend instead of the mcp storage
• Process a vCon, verify rows in vcons / parties / dialog / analysis / attachments
• Kill Postgres briefly, confirm the link retries and recovers without losing the vCon