I have a fully designed, working HTML prototype of a SaaS web app and need a developer to build the backend and make it fully functional. The platform is a social media scheduling tool for a niche professional audience in the UK. Users sign up, an AI assistant generates compliant content for them, they approve it, and it gets scheduled to their social media accounts. What I need built: ∙ Authentication — magic link login (no passwords), using Supabase Auth ∙ Database — user accounts, post history, audit logs (PostgreSQL via Supabase) ∙ AI integration — Anthropic Claude API to generate content based on user briefs ∙ Payments — Stripe subscriptions (4 plan tiers, monthly and annual, GBP, Apple Pay and Google Pay) ∙ File uploads — image uploads stored in Supabase Storage ∙ Social media publishing — OAuth connections to LinkedIn, Facebook, Instagram, X/Twitter, TikTok, WhatsApp Channels and YouTube Shorts via their official APIs ∙ Email — magic link and notification emails via Resend Tech stack preference: Next.js (React), Vercel hosting, Supabase, Stripe, Anthropic API What I will provide: ∙ Complete working HTML prototype (the full UI, all pages, all user flows) ∙ Written developer brief with database schema, feature specs and API requirements ∙ All design decisions already made — you are building the backend only Important: The platform handles personal data for regulated professionals in the UK. FCA compliance and audit trail logging are part of the spec. Budget: Open to quotes — please provide a breakdown by phase. I want an MVP first (auth, signup, AI generation, payments) before the full social publishing build. Please share: Examples of similar SaaS projects you have built, your experience with Supabase and Stripe, and your timeline estimate for an MVP.