docs: update directory layout, document NEXT_PUBLIC_SITE_URL, scripts and fix formatting (#253, #254, #255, #256)

[ghzhost]

Description

Closes #253, closes #254, closes #255, closes #256.

This PR brings README.md and .env.example up to date with the actual project structure and capabilities:

1. Directory layout (README.md's Directory layout section is stale — it omits context/, hooks/, components/dashboard/, and several lib/ files entirely #254): Updates the tree under src/ to accurately include context/, hooks/, components/dashboard/, and the missing lib/ modules (adapters.ts, auth.ts, env.ts, markdown.ts).
2. Document NEXT_PUBLIC_SITE_URL (NEXT_PUBLIC_SITE_URL, read by sitemap.ts, is undocumented in both .env.example and README's environment variables table #256): Documents NEXT_PUBLIC_SITE_URL in both .env.example and the Environment variables table in README.md.
3. Document missing scripts (README.md's Scripts table omits npm test, npm run test:watch, and npm run verify:env even though verify:env runs in CI and test is a working, documented package.json script #253): Adds rows for npm test, npm run test:watch, and npm run verify:env in README.md's Scripts table.
4. Fix stray bullet before <img> (README.md has a stray empty markdown bullet directly before an unindented <img> tag, breaking the repo-links list rendering #255): Removes stray bare bullet - and formats image spacing cleanly.

Validation

• npm run lint passes with 0 warnings/errors.
• npm run build succeeds cleanly.

[vercel]

Someone is attempting to deploy a commit to the chonilius' projects Team on Vercel.

A member of the Team first needs to authorize it.