feat(turbo): turbo gen feature generator (Phase 1, single-entity)

Adds `pnpm turbo gen feature` to scaffold a Lazar-conformant feature
package matching the navigation reference shape: entity + Zod schema,
single use case (`get<Entity>`), controller, mock + Payload-stub real
repository (with span + capture), DI module/container/symbols, and tRPC
router with full BAD_REQUEST/NOT_FOUND error mapping. The generated
`bind-production.ts` and `bind-dev-seed.ts` compose the post-R44
`withSpan(tracer, opts, withCapture(logger, tags, factory(deps)))`
sandwich at bind time.

Verified by generating a sample `packages/example/` feature and running
`pnpm --filter @repo/example lint typecheck test` — all three pass
(9 test files, 25 tests). Cleaned up after verification so no example
package is committed.

Phase-1 limitations (documented in `docs/guides/scaffolding-a-feature.md`
and printed by the generator on success): no Payload CMS templates, no
React Query helpers, faker-driven factories left as stubs, single
entity / single use case, and aggregator wiring (core-api/root,
apps/web-next bindAll) is left as a manual checklist.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/guides/scaffolding-a-feature.md

@@ -0,0 +1,101 @@
+# Scaffolding a feature
+
+`turbo gen feature` produces a Lazar-conformant feature package under
+`packages/<name>/` matching the shape of the reference `navigation` feature.
+
+## Invoking the generator
+
+Interactive (recommended for first runs — Plop will prompt for each value):
+
+```bash
+pnpm turbo gen feature
+```
+
+Non-interactive (positional bypass — order matches the prompts in
+`turbo/generators/config.ts`):
+
+```bash
+pnpm turbo gen feature --args <name> <Entity> <entities-plural>
+```
+
+| Position | Prompt | Example | Conventions |
+|---|---|---|---|
+| `<name>` | Feature package name | `widgets` | `kebab-case`, becomes `@repo/<name>` and `packages/<name>/` |
+| `<Entity>` | Entity name | `Widget` | `PascalCase` singular, drives class/symbol/use-case names |
+| `<entities-plural>` | Entity plural slug | `widgets` | `kebab-case`, used for the future Payload collection slug |
+
+Example end-to-end:
+
+```bash
+pnpm turbo gen feature --args widgets Widget widgets
+pnpm install                              # link the new workspace package
+pnpm --filter @repo/widgets lint typecheck test
+```
+
+## What it generates
+
+- Package files: `package.json`, `tsconfig.json`, `vitest.config.ts`,
+  `eslint.config.js`, `turbo.json`, `AGENTS.md`
+- One entity (`src/entities/models/<entity>.ts`) with a Zod schema +
+  unit test
+- One use case (`src/application/use-cases/get-<entity>.use-case.ts`) with
+  exported input/output schemas, factory function, and tests
+- One controller (`src/interface-adapters/controllers/get-<entity>.controller.ts`)
+  with the canonical safeParse → presenter shape
+- Mock + real repository (`src/infrastructure/repositories/<entity>.repository{,.mock}.ts`).
+  Both wrap calls in `tracer.startSpan`; the real repo also calls
+  `logger.captureException` on errors. The real repo body is a Phase-1
+  stub that returns `null` until you wire a Payload collection.
+- DI: `symbols.ts`, `module.ts`, `container.ts`, plus
+  `bind-production.ts` and `bind-dev-seed.ts` that compose
+  `withSpan(tracer, opts, withCapture(logger, tags, factory(deps)))` at
+  bind time (post-R44 sandwich pattern)
+- tRPC integration: `procedures.ts` (feature-scoped error middleware) and
+  `router.ts` exposing `get<Entity>` with full router tests including
+  `BAD_REQUEST` / `NOT_FOUND` mapping
+- Contract suite (`__contracts__/`), dev seed (`__seeds__/dev.ts`), and
+  empty stubs for `__factories__/` and `ui/`
+
+## Phase-1 scope (intentionally limited)
+
+The generator does NOT yet emit:
+
+- Payload CMS collection / global templates (`integrations/cms/**`)
+- React Query option builders (`ui/query.ts`)
+- Faker-driven `defineFactory<Entity>` factories (only stubs)
+- Multi-entity / multi-use-case (one `get<Entity>` only)
+- Aggregator wiring across the monorepo
+
+Add these by hand once the entity stabilises. The generator's stub files
+clearly mark each `TODO`.
+
+## Manual aggregator wiring (printed on success)
+
+After running the generator, hand-edit these files to mount the new
+feature on the app's runtime composition graph:
+
+1. **`apps/web-next/src/server/bind-production.ts`** — import
+   `bindProduction<Name>` and `bindDevSeed<Name>` and call them from the
+   `bindAll()` dispatcher (production branch + dev-seed branch).
+2. **`packages/core-api/src/root.ts`** — import `<name>Router` from
+   `@repo/<name>/api` and mount it on the app router.
+3. **`packages/core-api/package.json`** — add `"@repo/<name>": "workspace:*"`
+   to dependencies.
+4. **`apps/web-next/package.json`** — add `"@repo/<name>": "workspace:*"`
+   to dependencies.
+5. **(Later) Payload CMS** — add a collection at
+   `packages/<name>/src/integrations/cms/collections/<entities-plural>.ts`
+   and register it in `packages/core-cms/...`.
+6. **Verify**: `pnpm --filter @repo/<name> lint typecheck test`
+
+The same checklist is printed by the generator when it finishes.
+
+## Cross-links
+
+- `CLAUDE.md` — Key Conventions (factory-style use cases, `.toDynamicValue()`,
+  schemas-in-use-case, three binding modes per feature, span + capture sandwich)
+- `packages/navigation/AGENTS.md` — canonical reference shape the templates mirror
+- `docs/architecture/vertical-feature-spec.md` — design rationale for the layout
+- `docs/decisions/adr-012-lazar-conformance.md` — file naming + factory pattern
+- `docs/decisions/adr-013-input-output-unification.md` — schemas-in-use-case + presenter
+- `docs/decisions/adr-014-instrumentation-sentry.md` — span + capture wiring (R41–R44)