Default pgstrap generate to PGlite

[partyplatter08-lab]

Summary

• default pgstrap generate to run migrations in an in-memory PGlite database, so bun run db:generate does not require a running Postgres service
• keep external Postgres generation available with pgstrap generate --no-pglite
• restore DATABASE_URL and close the temporary PGlite/socket resources after generation
• update the PGlite generation test and README to match the new default

Validation

• npx --yes bun test
• npx --yes bun run format:check
• npx --yes bun run build
• node dist/cli.cjs generate --help

@algora-pbc /claim #2