fix: Refactor PrismaNeon initialization to use PoolConfig instead of Pool directly

[rnwolfe]

Description

This PR fixes a runtime error caused by passing a Pool instance into the PrismaNeon adapter instead of a PoolConfig object. The adapter expects a configuration object (with a connectionString), but the code constructed and passed a Pool, which lacks the expected connectionString property. Prisma's client then fell back to default host/user values and produced the runtime error:

“No database host or connection string was set, and key parameters have default values (host: localhost, user: ryan, db: ryan, password: null)...”

The change updates the PrismaNeon initialization to pass the expected PoolConfig object with the connectionString taken from DATABASE_URL.

Related Issues

Closes #643

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my code.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation, if necessary.
• I have added tests that prove my fix is effective or my feature works. I verified manually.
• New and existing tests pass locally with my changes.

Notes:

• This fix is small and targeted; it should not affect other database behavior because it only changes how the Neon adapter is constructed.
• I validated that pnpm migrate works and confirmed the root cause and fix in issue comments.

Screenshots (if applicable)

N/A

Additional Notes

Root cause and reproduction details are available in the original issue: #643

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