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>

turbo/generators/templates/feature/src/application/use-cases/get-entity.use-case.test.ts.hbs

@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+import { ZodError } from "zod";
+import { get{{pascalCase entity}}UseCase } from "@/application/use-cases/get-{{kebabCase entity}}.use-case";
+import { Mock{{pascalCase entity}}Repository } from "@/infrastructure/repositories/{{kebabCase entity}}.repository.mock";
+import { {{pascalCase entity}}NotFoundError } from "@/entities/errors/{{kebabCase entity}}";
+
+describe("get{{pascalCase entity}}UseCase", () => {
+  it("returns the seeded {{camelCase entity}} by id", async () => {
+    const repo = new Mock{{pascalCase entity}}Repository();
+    const useCase = get{{pascalCase entity}}UseCase(repo);
+    const result = await useCase({ id: "seed-1" });
+    expect(result.id).toBe("seed-1");
+    expect(result.name).toBeTypeOf("string");
+  });
+
+  it("throws {{pascalCase entity}}NotFoundError when repository returns null", async () => {
+    const repo = new Mock{{pascalCase entity}}Repository(new Map());
+    const useCase = get{{pascalCase entity}}UseCase(repo);
+    await expect(useCase({ id: "missing" })).rejects.toBeInstanceOf(
+      {{pascalCase entity}}NotFoundError,
+    );
+  });
+
+  it("throws ZodError when repository returns malformed data", async () => {
+    const malformedRepo = {
+      get{{pascalCase entity}}: async () => ({ id: "", name: "x" }) as never,
+    };
+    const useCase = get{{pascalCase entity}}UseCase(malformedRepo);
+    await expect(useCase({ id: "anything" })).rejects.toBeInstanceOf(ZodError);
+  });
+});