[ISSUE-027] AI Meal Plan Generation Service

## Phase 5: AI Infrastructure & Meal Planning (Weeks 7-9)

### Description
Integrate RAG service with meal plan API
Implement meal plan generation logic
Consider user preferences, inventory, schedule constraints
Generate shopping list from meal plan
Calculate estimated costs
Provide AI reasoning for recommendations

### Dependencies
- #025
- #026

### Can Work in Parallel With
- #028

Start by reading dependency issues #025 and #026, then locate the meal plan API and RAG service entry points. Define the integration around preferences, inventory, schedule constraints, shopping-list generation, estimated costs, and recommendation reasoning; done means these requirements are implemented and verifiable.

Written by the indexing model from the issue text.