Add public recipe read endpoint by slug #1136

Goal

Add a public (unauthenticated) endpoint that serves a recipe by its slug, enabling public sharing of published recipes.

Spec reference

docs/specs/recipe-creation-target-architecture.md — §"Public recipe endpoints"

Implementation notes

• GET /public/recipe/{slug} — in the /public route group from E6.5; no RequireAuthorization()
• Resolves active RecipePublication by slug (where UnpublishedAtUtc IS NULL)
• Returns RecipeDetail DTO (same shape as authenticated detail)
• 404 if no active publication for slug
• Emits RecipeViewed outbox event (unauthenticated variant): { recipeId, viewerUserId: null, isAuthenticated: false, timestamp }

Acceptance criteria

• Valid slug returns RecipeDetail without authentication
• Unpublished slug returns 404
• RecipeViewed outbox event written with isAuthenticated: false

Testing

• Integration tests: valid slug, unpublished slug, never-published slug all handled correctly
• Integration test: RecipeViewed event written on public read

Part of#1103