feat: add `database-neon` module

[ronak-create]

Summary

Add Neon (serverless Postgres) as a database option, alongside the existing database-postgresql module.

Why

Neon is the dominant serverless Postgres provider — used heavily with Next.js and Vercel deployments.
It has a distinct client (@neondatabase/serverless) optimised for connection pooling in serverless environments where long-lived pg pools aren't viable.

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Files to generate

• src/db/client.ts — Neon serverless client with pool setup
• src/db/migrations/001_init.sql
• .env.example — with DATABASE_URL (Neon connection string format)

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Implementation hints

• Add packages/modules/src/database/neon.ts
  → use supabase.ts or postgresql.ts as the template

• Key dependency:

  • @neondatabase/serverless

• The client.ts should:

  • use neon() for single queries
  • use Pool for transactions

• Register in same places as other database modules

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Contributor guidance

Refer to CONTRIBUTING.md → "Adding a New Module"

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Acceptance criteria

• foundation create lists Neon as a database option
• Generated client.ts type-checks cleanly
• .env.example contains DATABASE_URL=postgresql://...
• Snapshot test added