Switch from create-elm-app to Parcel and add CI/CD workflows

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Setup Node
+        uses: actions/setup-node@v6
+        with:
+          node-version-file: .tool-versions
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run Elm tests
+        run: npx elm-test

.github/workflows/deploy.yml

@@ -0,0 +1,52 @@
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Only allow one deployment at a time, but don't cancel in-progress runs
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Setup Node
+        uses: actions/setup-node@v6
+        with:
+          node-version-file: .tool-versions
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build
+        run: npm run build
+
+      - name: Upload Pages artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: dist
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4

.gitignore

@@ -10,6 +10,8 @@
 
 # Distribution
 build/
+dist/
+.parcel-cache/
 
 # elm-package generated files
 elm-stuff

.parcelrc

@@ -0,0 +1,6 @@
+{
+  "extends": ["@parcel/config-default"],
+  "transformers": {
+    "*.elm": ["@parcel/transformer-elm"]
+  }
+}

.tool-versions

@@ -0,0 +1 @@
+nodejs 24

README.md

@@ -7,12 +7,39 @@
 
 App to demonstrate gravitational slingshot maneuvers.
 
-https://adamnfish.github.io/luna/index.html
+https://adamnfish.github.io/luna/
+
+## Local development
+
+Install dependencies:
+
+```sh
+npm install
+```
+
+Start the dev server (available at http://localhost:1234):
+
+```sh
+npm start
+```
+
+Run the Elm tests:
+
+```sh
+npm test
+```
+
+Build for production (output in `dist/`):
+
+```sh
+npm run build
+```
 
 ## Source code
 
 This is an Elm application built using
-[create-elm-app](https://github.com/halfzebra/create-elm-app). The
+[Parcel](https://parceljs.org/) with
+[@parcel/transformer-elm](https://github.com/nicois/parcel-transformer-elm). The
 program runs from [`src/Main.elm`](src/Main.elm), which provides the
 initial state and browser integration (including a subscription to
 `requestAnimationFrame`). Updates to the state come from messages,