feat: use pglite to avoid requiring postgres when generating types

[MrAnderson323]

When running bun run db:generate, users no longer need a running PostgreSQL instance. Instead, the type generation process spins up an in-process PGlite instance, applies the schema migrations, introspects the resulting schema, and generates types — all without any external dependencies.

This uses @electric-sql/pglite to run an ephemeral in-memory PostgreSQL-compatible database for schema introspection during type generation.

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Closes #2