Use PGlite by default for CLI generation

[ninomaaad]

bun run db:generate created by pgstrap init still selects the external PostgreSQL path unless --pglite is passed. Make CLI generation replay migrations in PGlite by default, so it creates the Zapatos declarations and SQL structure without a running PostgreSQL service. --no-pglite explicitly selects the existing configured-server path; programmatic callers retain their current default.

The temporary gateway binds to localhost and closes its sockets/database on success or failure. The schema dumper uses the temporary connection even when a higher-priority POSTGRES_URI is configured, then restores the original value. The CLI awaits generation so failures propagate through its command handler.

Closes #2.

Validation

• bun test --timeout 15000: 8 passed, 30 assertions. CLI tests build the package, initialize a fresh project and run its actual db:generate script with all connection URI variables pointing at an unavailable database. They check generated table/column content, explicit PostgreSQL opt-out, migration errors and output-write failure exit behavior.
• The new default-command and migration-error checks failed before the feature change. Existing tests passed after restricting the test gateway to localhost.
• bun run build, bun run format:check and git diff --check passed. Patch application checked against the base commit.

The live PostgreSQL success path and concurrent programmatic PGlite calls were not tested. PGlite-specific extension limitations remain; --no-pglite supports opting back into an existing server.

Prepared with AI assistance; the listed checks were executed locally.

/claim #2