docs(reflow): add web app screenshots, replace ASCII working-layout diagram
- Add reflow-empty.png and reflow-complete.png under reflow/assets
- use-the-web-app: show empty landing in "Upload a document"; replace
ASCII working-layout diagram with the completed-run screenshot
- process-your-first-pdf-with-the-web-app: show empty landing in
step 1 and the completed layout in step 5
Images reference raw.githubusercontent.com URLs on main so they render
on the Equalify Hub (which doesn't rewrite relative paths) as well as
directly on GitHub. Descriptive alt text + short captions included.
The assets/ folder is safe from being rendered as a doc category — the
hub's listing filter only pulls .md files.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>