Senior WordPress Developer & UI Assistant for Watch Platform

I am looking for a Senior WordPress Developer to build a custom backend architecture for an e-commerce platform (Montres Mania Paris). The main focus of this job is custom WordPress coding, alongside minor assistance with responsive UI layouts in Figma.
The core visual direction and desktop screens are ready. I need an experienced engineer to write the code and fine-tune mobile UI states.
Key Responsibilities:
1. Custom WordPress Engineering (Primary Focus - 80%):
Build a custom WordPress theme from scratch using PHP, JavaScript, HTML5, and CSS3 based on Figma specs.
Create custom post types, advanced fields (ACF), and backend data structures for product attributes (caliber, reference number, movement, production year).
Develop custom catalog filtering, search logic, and cart workflow directly within WordPress.
Optimize database queries, asset loading, and Core Web Vitals for maximum performance.
Perform full cross-browser testing, code debugging, and QA.
2. UI Adaptation & Polish (Secondary Focus - 20%):
Adapt provided desktop Figma screens into responsive mobile/tablet layouts prior to frontend coding.
Ensure pixel-perfect alignment between final design components and production code.
Requirements:
Proven expertise in custom WordPress theme/backend execution without heavy pre-built templates or page builders.
Deep knowledge of PHP, MySQL, JavaScript, HTML5, CSS3, and basic Figma usage.
Ability to write clean, scalable, and secure custom code.
High attention to performance benchmarks and technical stability.
Application Guidelines (Please answer when applying):
Share links to 2-3 custom WordPress sites you have personally coded.
Have you built custom e-commerce or complex catalog projects on WordPress before?
What exact technical roles did you perform on those projects?
How many active projects do you currently have, and what is your immediate availability?