chore: remove the leftovers of the Vite template

[ronjalh]

What

Removes the files and CSS that the Vite template left behind. Part of the peer feedback in #167.

• Deleted src/assets/hero.png, react.svg, vite.svg, src/App.css and public/icons.svg. None of them is imported or referenced anywhere in src/, index.html or the docs (checked with a search).
• Removed from src/index.css the rules and tokens that only the template used: .counter, #social .button-icon, --accent-bg, --accent-border, --social-bg and --shadow (nothing reads them).
• Updated the comment at the top of src/index.css, which said that the starter styles would go.

Not changed on purpose

The rest of the starter styles in src/index.css is still in use and changes how every page looks: the #root width and border, the h1/h2 sizes, p, code, and the --text, --bg, --border tokens on :root (including the dark block for visitors without a stored theme). Removing them is a visual change and needs a check of every page, so it is better as its own issue (it also touches #161 and #168).

Checked

• npm run build passes, tsc -b is clean and the frontend tests pass (402).
• The backend tests need a database and could not run in this clean worktree.

Closes #180

🤖 Generated with Claude Code

[anettkva]

Nice cleanup! tsc, lint, Prettier, the build and all 312 frontend tests pass, and nothing uses the deleted files or CSS variables.

Before merge: the README still mentions src/App.css (line 143: "A rule in src/index.css or src/App.css therefore overrides a utility class…"). Since this PR deletes it, that line should reflect that:)

Generated with Claude Code, from my review.