[EXTRACT] ShoppingListService - Rip shopping list operations from monolith

[democratize-technology-code-reviewer]

🔪 Extraction Target

Extract all shopping list operations from the 19,843-line index.mjs into a focused ShoppingListService class. Clean cut.

📁 Methods to Extract

// All of these get ripped out and moved to ShoppingListService
getShoppingList()
getShoppingLists()
addToShoppingList()
removeFromShoppingList()
clearShoppingList()
updateShoppingListItem()
// ... and any other shopping-list-related methods

🎯 Definition of Done

• Create services/ShoppingListService.js extending BaseService
• Extract ALL shopping list methods from index.mjs
• File size < 500 lines (enforced by linter)
• All existing tests pass WITHOUT modification
• Add JSDoc comments for each method
• No deprecated methods or compatibility layers
• Update all imports/references in index.mjs
• Zero regression - identical functionality

⚡ Implementation

// services/ShoppingListService.js
export class ShoppingListService extends BaseService {
  async getShoppingList() {
    // Direct copy from index.mjs - no changes
  }
  
  async addToShoppingList(productId, amount, listId) {
    // Direct copy from index.mjs - no changes
  }
  
  // ... rest of shopping list methods
}

🚫 NOT in Scope

• Backward compatibility
• Deprecation warnings
• Proxy methods in GrocyClient
• Changing method signatures
• Adding new features

💀 Breaking Changes

Yes. Evolve.

Related to

Parent issue: #11