fix: fall back to pglite for type generation

[sclee980528-prog]

Problem

pgstrap generate still required a reachable Postgres server unless users remembered to pass --pglite. That means the default bun run db:generate script scaffolded by pgstrap could fail on a machine without local Postgres running.

Approach

• Make generate default to an auto mode: use the configured Postgres database when it is reachable, and fall back to PGlite only when the connection is unavailable.
• Keep both explicit paths:
  • pgstrap generate --pglite forces the embedded PGlite flow.
  • pgstrap generate --no-pglite requires real Postgres and disables fallback.
• Reuse the existing PGlite plus pg-gateway wire-protocol bridge so Zapatos and pg-schema-dump can introspect through normal Postgres clients.
• Restore DATABASE_URL and close the temporary bridge server, sockets, and PGlite instance after generation.
• Add regression coverage for default generation when Postgres is unavailable.

Verification

• npm_config_cache=/private/tmp/bounty-pgstrap-npm npx --yes bun@1.2.21 test
  • 4 pass, 0 fail
• npm_config_cache=/private/tmp/bounty-pgstrap-npm npx --yes bun@1.2.21 run format:check
  • passed
• npm_config_cache=/private/tmp/bounty-pgstrap-npm npx --yes bun@1.2.21 run build
  • passed, including DTS build
• git diff --check
  • passed
• Confirmed no postgres or postmaster process was running with pgrep -fl 'postgres|postmaster'.
• Created a fixture project and ran bun run db:generate with DATABASE_URL and PG* env vars unset.
  • It printed Postgres unavailable; generating with PGlite.
  • It generated src/db/zapatos/schema.d.ts.
  • It generated src/db/structure/public/tables/widgets/table.sql.
• Compared auto-fallback output against explicit --pglite output for the same fixture.
  • Zapatos diff: 0
  • Structure diff: 0

Usage

Default behavior now works without local Postgres:

bun run db:generate

Force PGlite:

pgstrap generate --pglite

Require real Postgres:

pgstrap generate --no-pglite

@algora-pbc /claim #2