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/jsconfig.json

@@ -4,10 +4,6 @@
     "allowJs": true,
     "checkJs": false,
     "module": "esnext",
-    "moduleResolution": "bundler",
-    "paths": {
-      "$app/types": ["./.svelte-kit/types/index.d.ts"],
-      "@/*": ["./*"]
-    }
+    "moduleResolution": "bundler"
   }
 }