Add backend to existing web app - auth, database, Whisper voice, PDF export

I have an existing front end and I need a working backend behind it. Fixed price, clearly defined scope. ABOUT THE PROJECT FormSync is a web app for Australian trade businesses (rope access, plumbing, electrical) to create site safety paperwork - SWMS (Safe Work Method Statements) and daily pre-start checks - from a phone on site. The headline feature is voice: a worker describes the job and hazards out loud, and AI generates the SWMS for review and sign-off. The front end already exists as static HTML/JS and is live on Netlify. It currently has a mock login and nothing persists. I need it turned into a real multi-tenant app so companies can use it every day. I will provide the full source. SCOPE - FOUR DELIVERABLES 1. Authentication and company accounts - Company signs up and gets its own workspace (multi-tenant, strict data isolation between companies) - Company admin can add workers as users. Roles: admin, worker - Replace the existing mock login with real auth 2. Document persistence and sync - SWMS and pre-start documents save to a database, tied to the company and the user who created them - Documents appear in "My Documents" on any device the user logs in from - Company settings persist: workers, sites/jobs, client details - The existing front-end fields and document structure are the schema starting point 3. Voice to SWMS (Whisper integration) - Record audio in the browser on mobile - iOS Safari and Android Chrome both must work - Send audio to OpenAI Whisper, pass the transcript into the existing SWMS generation prompt (Anthropic API, already wired on the front end), return the generated SWMS to the form - API keys server-side only, never in the browser 4. PDF export and send - Server-side PDF generation of a completed SWMS or pre-start - Download, and email to a client address from within the app - Signature capture on the SWMS, included in the PDF OUT OF SCOPE Payments/Stripe, timesheets, Xero, fleet, inventory, calendar, native mobile apps. These exist as demo screens - leave them alone. TECHNICAL - I am open on stack. Supabase (Postgres + auth + storage) with the existing front end is my default suggestion - propose an alternative if you have a strong reason - Front end stays on Netlify unless there is a good reason to move - Code delivered in a Git repo I own, with a README covering setup, environment variables and deployment - Handover call at the end walking me through the admin side WHAT I PROVIDE Full existing source code, OpenAI and Anthropic API keys (billing on my accounts), domain and Netlify access, and fast answers - I am the domain expert and I will be available daily. TO QUOTE, PLEASE SEND 1. Your fixed price for the four deliverables 2. Your proposed stack in a couple of sentences 3. Timeline with milestones. I want auth + persistence delivered first so I can start a trial with a real company while the rest is built 4. One or two examples of similar work (auth + database + third-party API) Please start your proposal with the word ROPE so I know you have read this.