Should you build your own Jasper?

Build me a personal marketing-copy generator to replace Jasper. Requirements:

- A local web app: Node + Express + better-sqlite3 on localhost:4850, plain
  server-rendered forms, no frontend framework.
- A brand/ folder of Markdown files: voice.md (tone rules, banned words),
  audience.md, product.md. Every generation prepends these to the prompt
  automatically.
- Template library in SQLite: blog outline, landing-page hero, product description,
  cold email, tweet thread. Each template is a prompt with {{variables}} filled in
  from a small form.
- Calls the Anthropic or OpenAI API (key and model name in .env), streams into the
  page, and always produces 3 variants side by side.
- Every output saved with template, inputs, chosen variant, and a campaign label;
  past outputs browsable and searchable by campaign.
- A rewrite box: paste any draft, get it back in my brand voice.
- Everything stays on my machine except the LLM calls. No accounts, no telemetry.
- Out of scope: team collaboration, approval workflows, and multi-writer brand
  governance. This is a one-person tool.
- README: .env keys and how to tune the brand files, that is where the quality lives.