Should you build your own Canva?

Build me a small canvas design editor to replace Canva Pro. Requirements:

- A local web app: Fabric.js on a canvas element with vanilla JS, and a tiny
  Express server for saving and export. Script tags only, no build step.
- Canvas presets: Instagram post 1080x1080, story 1080x1920, X header
  1500x500, A4 poster, plus a custom-size dialog.
- Editing: text using my local fonts, image upload, rectangles and lines, a
  layer list with reorder, align-to-center helpers, and snap guides at the
  canvas center.
- A brand panel loaded from brand.json: my 4 colors and 2 fonts as one-click
  swatches.
- Every design serializes to designs/<name>.json and reopens exactly;
  duplicate-as-template is the template system. Ship 3 starter designs.
- Export PNG at 1x and 2x via Fabric's toDataURL, and PDF by printing the
  canvas page with Playwright.
- All files local, no accounts, no telemetry.
- Out of scope: stock photos, AI image tools, and collaboration. The asset
  library is what the Pro fee buys, I bring my own images.
- README: how to add fonts and where designs live on disk.