Add GitHub Actions workflow for JOSS PDF generation

Introduced a GitHub Actions workflow to automate the generation of JOSS paper drafts. This workflow triggers on pushes to the relevant files and creates a draft PDF, which is then uploaded as an artifact.

.github/workflows/paper.yml

@@ -0,0 +1,27 @@
+name: JOSS PDF Generation
+
+on:
+  push:
+    paths:
+      - 'paper/**'
+      - '.github/workflows/paper.yml'
+
+jobs:
+  paper:
+    runs-on: ubuntu-latest
+    name: Paper Draft
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Build draft PDF
+        uses: openjournals/openjournals-draft-action@v1
+        with:
+          journal: joss
+          paper-path: paper/paper.md
+
+      - name: Upload PDF
+        uses: actions/upload-artifact@v4
+        with:
+          name: paper
+          path: paper.pdf