feat: default to pglite for db:generate without requiring postgres

[samsiroo]

Fixes #2
@algora-pbc /claim #2

Summary

Default pglite to true when running generate / db:generate, enabling in-memory schema and type generation out of the box without requiring an active PostgreSQL daemon running in the background.

Users targeting an external PostgreSQL database can explicitly opt out using the --no-pglite flag.

Changes

• src/cli.ts: Default --pglite flag to true with support for explicit --no-pglite negation (argv.pglite !== false).
• src/generate.ts: Default pglite parameter to true.
• tests/generate.pglite.test.ts: Verify generate() runs with PGlite by default without requiring pglite: true explicitly passed.
• README.md: Update documentation to reflect default in-memory behavior and --no-pglite opt-out.

Verification

• bun test: All test suites pass.
• bun run build: Clean compilation with tsup.