feat(pgpm): default pgpm init to no extensions (opt-in via flags)

[pyramation]

Summary

pgpm init no longer forces an extensions decision. A bare pgpm init now scaffolds a module with no extensions — its .control has no requires = line — matching the zero-config init of comparable tools (sqitch, prisma, drizzle, dbmate, supabase, ...). Extensions become an explicit, lazy opt-in.

This is PR A of the extensions-DX cleanup. plpgsql is always present in Postgres (requiring it was noise) and uuid-ossp is legacy (gen_random_uuid() is core since PG13), so neither belongs in the default scaffold. Follow-ups: PR B hardens pgpm extension as the canonical enable-later path (non-destructive .control rewrite + --add/--set/--remove); PR C refreshes the tutorials.

What changed

The forced checkbox in pgpm/cli/src/commands/init/index.ts was:

// before: always prompted, pre-checked, and required
moduleQuestions.push({ name: 'extensions', type: 'checkbox',
  required: true, default: ['plpgsql', 'uuid-ossp'] });

Now the question is only added when the user opts in, and never defaults anything:

if (typeof argv.extensions === 'string')            // normalize `--extensions a,b`
  argv.extensions = argv.extensions.split(',').map(s => s.trim()).filter(Boolean);

const extensionsProvided   = argv.extensions !== undefined;      // `--extensions a,b`
const wantExtensionsPrompt = Boolean(argv.withExtensions || argv['with-extensions']);

if (isPgpmTemplate && project.workspacePath &&
    (extensionsProvided || wantExtensionsPrompt)) {
  moduleQuestions.push({ name: 'extensions', type: 'checkbox',
    allowCustomOptions: true, default: [] });   // no `required`, no default
}

So:

• pgpm init → no extensions (no requires line).
• pgpm init --extensions uuid-ossp,citext → non-interactive knob (unchanged extraction path; also the back-compat bridge).
• pgpm init --with-extensions → interactive picker, empty default, not required.

No core changes needed — generateControlFileContent already omits requires = for an empty list, and deploy already skips CREATE EXTENSION when there are none.

Tests

• Added regression test: bare pgpm init produces a .control with no requires line and getRequiredModules() === [].
• Existing init/install/extensions/package suites pass unchanged — they pass extensions explicitly, so they exercise the opt-in path. Snapshots regenerated for the new test only.

Note: repo-wide pnpm lint currently fails on an unrelated pre-existing ESLint v9 config issue (no eslint.config.js); tsc --noEmit and the package build are clean.

Link to Devin session: https://app.devin.ai/sessions/424b76f81a60499493ac946b57136ad9
Requested by: @pyramation

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