Frontend developer
Turns the design into something that works in a browser, at any screen size, with a keyboard, on a slow connection. This is the person whose work decides whether the site loads quickly.
When your project needs this person
On any project that is not a pure template.
What happens when they are missing
The site matches the design only on the designer’s screen. On a phone the text overflows, buttons are tiny, and the page weighs several megabytes because nobody compressed the images.
How this appears in an offer
Usually hidden inside "development". If the price is very low, this is most often the work that was skipped and replaced with an off-the-shelf theme.
What they do NOT do
Does not decide what the page says and is not responsible for content structure.