test(recipe-routes): add scaffolding baseline

docs/architecture/recipe_routes.md

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+# Recipe route scaffolding
+
+The recipe HTTP stack is being migrated to mirror the shared model routing
+architecture.  The first phase extracts the registrar/controller scaffolding so
+future handler sets can plug into a stable surface area.  The stack now mirrors
+the same separation of concerns described in
+`docs/architecture/model_routes.md`:
+
+```mermaid
+graph TD
+    subgraph HTTP
+        A[RecipeRouteRegistrar] -->|binds| B[BaseRecipeRoutes handler owner]
+    end
+    subgraph Application
+        B --> C[Recipe handler set]
+        C --> D[Async handlers]
+        D --> E[Services / scanners]
+    end
+```
+
+## Responsibilities
+
+| Layer | Module(s) | Responsibility |
+| --- | --- | --- |
+| Registrar | `py/routes/recipe_route_registrar.py` | Declarative list of every recipe endpoint and helper that binds them to an `aiohttp` application. |
+| Base controller | `py/routes/base_recipe_routes.py` | Lazily resolves shared services, registers the server-side i18n filter exactly once, pre-warms caches on startup, and exposes a `{handler_name: coroutine}` mapping used by the registrar. |
+| Handler set (upcoming) | `py/routes/handlers/recipe_handlers.py` (planned) | Will group HTTP handlers by concern (page rendering, listings, mutations, queries, sharing) and surface them to `BaseRecipeRoutes.get_handler_owner()`. |
+
+`RecipeRoutes` subclasses the base controller to keep compatibility with the
+existing monolithic handlers.  Once the handler set is extracted the subclass
+will simply provide the concrete owner returned by `get_handler_owner()`.
+
+## High-level test baseline
+
+The new smoke suite in `tests/routes/test_recipe_route_scaffolding.py`
+guarantees the registrar/controller contract remains intact:
+
+* `BaseRecipeRoutes.attach_dependencies` resolves registry services only once
+  and protects the i18n filter from duplicate registration.
+* Startup hooks are appended exactly once so cache pre-warming and dependency
+  resolution run during application boot.
+* `BaseRecipeRoutes.to_route_mapping()` uses the handler owner as the source of
+  callables, enabling the upcoming handler set without touching the registrar.
+* `RecipeRouteRegistrar` binds every declarative route to the aiohttp router.
+* `RecipeRoutes.setup_routes` wires the registrar and startup hooks together so
+  future refactors can swap in the handler set without editing callers.
+
+These guardrails mirror the expectations in the model route architecture and
+provide confidence that future refactors can focus on handlers and use cases
+without breaking HTTP wiring.