extract(plop-templates): unfork, publish as create-operant-app CLI in packages/boilerplate

## Problem
`tools/plop-templates/` exists in both repos with real divergence (README.md.hbs, route.ts.hbs, route.test.ts.hbs differ). The extraction plan called for `packages/boilerplate/` becoming a `create-operant-app` CLI. Nothing there yet.

## Scope
1. Merge divergent templates; take Portico's `route.ts.hbs` as base (battle-tested), overlay any Ledger improvements.
2. Move to `packages/boilerplate/` in operant-studio with a proper CLI entry: `create-operant-app <name>` scaffolds a new app.
3. First real target: Piper DX repo scaffolded via `create-operant-app piper-dx` — proves the CLI works.
4. Delete `tools/plop-templates/` from both Portico and Ledger; reference the CLI or the published package for one-off scaffolds.

## Depends
- Nothing hard, but OPER-7 makes it cleaner because scaffolded apps can depend on `@operant/eslint-plugin`.

## Blocks
- Piper DX kickoff.

## Verification
- `pnpx create-operant-app test-app` produces a working Next.js app skeleton with Ledger client, RBAC, ESLint plugin, and Prisma database package all wired.
- App boots locally.
- App can register with Ledger.