Create a new Convex mutation function with proper validators and auth
# Create Convex Mutation Create a new Convex mutation function following best practices: 1. Use the new function syntax with `mutation` from "./_generated/server" 2. Include argument validators using `v` from "convex/values" 3. Include return validators (use `v.null()` if no return) 4. Add authentication check if needed using `getAuthUserId` 5. Use proper TypeScript types with `Id<>` and `Doc<>` The mutation should be for: $ARGUMENTS Follow these rules: - ALWAYS include `args` and `returns` validators - Check authentication with `getAuthUserId` for protected mutations - Use `ctx.db.inse...