chore(web-player): add prettier and eslint

Flat ESLint config with typescript-eslint and eslint-plugin-svelte,
Prettier with the svelte and tailwindcss plugins. Adds the format and
lint scripts.

Three rules are off on purpose: no-navigation-without-resolve (the app
is served at the root, there is no base path), prefer-svelte-reactivity
(the Set and URLSearchParams uses are local computations, not reactive
state) and no-unused-expressions in .svelte only, where reading a rune
on its own line is how an $effect registers a dependency.

web-player/.prettierignore

@@ -0,0 +1,11 @@
+.DS_Store
+node_modules
+build
+.svelte-kit
+package
+.env
+.env.*
+!.env.example
+package-lock.json
+src/lib/api/schema.d.ts
+static