Phase 13: Account sync API for loadout favorites

[elfensky]

Summary

Server actions to sync loadout favorites with the user's account via the existing Settings JSON field.

Parent: #162 | Depends on: #345 (localStorage favorites)

Architecture

Two server actions:

• syncLoadoutFavorites(favorites) — overwrites server favorites with client data
• getLoadoutFavorites() — returns server favorites

Stores in Settings.settings.loadouts JSON path. Client merges localStorage + server on page load (union by hash, client wins on conflict).

Silently falls back to localStorage when auth is disabled or user not signed in — no error states.

Files

• CREATE src/features/loadout/actions.mjs — 'use server' actions with auth guard
• CREATE src/features/loadout/useLoadoutSync.mjs — client hook for merge logic
• MODIFY src/features/loadout/FavoritesList.jsx

Patterns to Follow

• src/db/queries/account.mjs for auth guard pattern
• tryCatch wrapper for all Prisma calls
• No new Prisma migration needed (Settings model with Json column already exists)

Size: M