feat: Supabase edge function example

[Chriztiaan]

This PoC takes the original write improvements PoC a step further and wedges the endpoint handling, mapper, and persistence logic into a Supabase edge function.

We get two benefits from this approach compared to the original SupabaseConnector plus Supabase backend:

• We move all translation/mapping logic from the client to the backend.
• We get proper transaction support without migrating off Supabase or managing a separate backend (enabling rollback on failure is something the Supabase JS SDK can't do today)

AI disclosure

This PR was created with the help of Claude Code. Help constitutes assistance in research, planning, and rough outline of implementation. Beyond having a hand in the implementation, I have also manually tested this work.