chore: remove Next.js and repoint CI at the SvelteKit layout

sync-data.yml now writes static/champions.json. This is the edit that had to
land with the deletion of public/: the workflow reports success regardless of
which path it writes, so a miss would have left the weekly sync green while
the live game 404'd on data load.

deploy.yml publishes build/ and passes BASE_PATH. Adds ci.yml, which runs
test, lint, and build on pull_request and pushes to main -- the repo had no
PR-triggered workflow before, so 'green before merge' was previously
unenforceable.

Deletes app/, components/, lib/, public/, next.config.mjs and
postcss.config.mjs, drops the Next and React dependencies, and swaps ESLint
onto eslint-plugin-svelte. sharp and unrs-resolver left pnpm's allowBuilds
because both arrived with Next and pnpm why now reports no dependents.

web/README.md

@@ -4,6 +4,8 @@ LoLdle-style League of Legends daily champion guessing game — data auto-update
 
 Live: https://tiennm99.github.io/loldle/
 
+Built with SvelteKit and Svelte 5, styled with Tailwind CSS, and prerendered to a static site deployed on GitHub Pages.
+
 ## Quick start
 
 ```bash
@@ -11,6 +13,18 @@ pnpm install
 pnpm dev
 ```
 
+## Commands
+
+```bash
+pnpm dev      # dev server
+pnpm build    # static build into build/
+pnpm preview  # serve the production build
+pnpm test     # unit tests
+pnpm lint     # eslint
+```
+
+Champion data lives in `static/champions.json` and is refreshed weekly by the sync workflow.
+
 ## License
 
 Apache-2.0 — see [LICENSE](LICENSE).