Modernize build tooling: migrate to @rollup/* plugins, Lit 3, HA-WS 9, ES module output

.browserslistrc

@@ -0,0 +1,3 @@
+unreleased versions
+last 7 years
+>= 0.05% and supports websockets

.github/workflows/build-check.yaml

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+name: Build Check
+
+on:
+  pull_request:
+  push:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install
+        run: npm ci
+
+      - name: Build
+        run: npm run build

.gitignore

@@ -1,5 +1,4 @@
 node_modules
-package-lock.json
 README.html
 *.DS_Store
 .vscode

.prettierignore

@@ -0,0 +1,4 @@
+node_modules
+dist
+package-lock.json
+package.json

eslint.config.mjs

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+import eslint from "@eslint/js";
+import tseslint from "typescript-eslint";
+
+export default tseslint.config(
+  eslint.configs.recommended,
+  ...tseslint.configs.recommended,
+  {
+    rules: {
+      "@typescript-eslint/no-explicit-any": "off",
+      "@typescript-eslint/explicit-function-return-type": "off",
+      "@typescript-eslint/no-empty-function": "off",
+      "@typescript-eslint/no-non-null-assertion": "off",
+      "@typescript-eslint/no-unused-vars": "off",
+      "@typescript-eslint/no-use-before-define": "off",
+      "@typescript-eslint/ban-ts-comment": "off",
+      "@typescript-eslint/no-empty-object-type": "off",
+      "no-unsafe-optional-chaining": "off",
+      "no-prototype-builtins": "off",
+      "no-cond-assign": "off",
+      "no-useless-escape": "off",
+      "no-case-declarations": "off",
+      "no-duplicate-case": "off",
+      "no-empty": "off",
+    },
+  },
+  {
+    ignores: ["dist/", "node_modules/", "rollup.config.mjs", "stats.html"],
+  }
+);