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/index.ts.hbs

@@ -0,0 +1,16 @@
+export type { {{pascalCase entity}} } from "./entities/models/{{kebabCase entity}}";
+export type { {{pascalCase name}}Router } from "./integrations/api/router";
+export { {{pascalCase entity}}NotFoundError } from "./entities/errors/{{kebabCase entity}}";
+export { InputParseError } from "./entities/errors/common";
+
+// Use case schemas + types
+export {
+  get{{pascalCase entity}}InputSchema,
+  get{{pascalCase entity}}OutputSchema,
+  type Get{{pascalCase entity}}Input,
+  type Get{{pascalCase entity}}Output,
+  type IGet{{pascalCase entity}}UseCase,
+} from "./application/use-cases/get-{{kebabCase entity}}.use-case";
+
+// Controller type aliases
+export type { IGet{{pascalCase entity}}Controller } from "./interface-adapters/controllers/get-{{kebabCase entity}}.controller";