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/.prettierrc

@@ -0,0 +1,14 @@
+{
+	"useTabs": true,
+	"singleQuote": true,
+	"trailingComma": "none",
+	"printWidth": 100,
+	"plugins": ["prettier-plugin-svelte", "prettier-plugin-tailwindcss"],
+	"tailwindStylesheet": "./src/routes/layout.css",
+	"overrides": [
+		{
+			"files": "*.svelte",
+			"options": { "parser": "svelte" }
+		}
+	]
+}