Extend create/update recipe endpoints to accept ingredients and steps

[dgee2]

Goal

Extend the recipe create and update endpoints to accept a full recipe payload including ingredients and steps.

Spec reference

docs/specs/recipe-creation-target-architecture.md — §"API changes required"

Implementation notes

• POST /api/recipe — creates recipe with ingredient and step collections; sets OwnerUserId from provisioned caller
• PUT /api/recipe/{recipeId} — updates recipe; owner check (403 if caller is not the owner)
• Service-layer logic: diff and upsert ingredient collection and step collection in a single transaction (replace collection by recipeId)
• Validate: Title non-empty; ingredient IngredientText and MeasureText non-empty; step InstructionText non-empty
• Accept zero ingredients / zero steps (valid minimal recipe)
• Return 409 if (OwnerUserId, Title) unique constraint would be violated

Acceptance criteria

• POST creates recipe with ingredients and steps in a single transaction
• PUT replaces ingredient/step collections atomically
• Owner check on PUT returns 403 for non-owners
• Validation errors return 400

Testing

• Unit tests for collection diff/upsert logic
• Integration tests: create, update with ingredient changes, non-owner update returns 403

Part of#1099