feat: support React 18 and 19 via peer dependencies

Widen peerDependencies from "^19" to "^18 || ^19" for react and
react-dom in eds-core-react, eds-lab-react, eds-data-grid-react, and
eds-utils. Add CI workflow to verify React 18 compatibility on PRs.

Verified locally: build, typecheck, and all 684 tests pass with React 18.

Author: pomfrida

.github/workflows/react18-compat.yaml

@@ -0,0 +1,51 @@
+name: React 18 compatibility
+permissions:
+  contents: read
+on:
+  pull_request:
+    branches:
+      - main
+    paths:
+      - 'packages/**'
+
+jobs:
+  setup:
+    uses: ./.github/workflows/_setup.yml
+    secrets: inherit
+    with:
+      cacheKey: ${{ github.sha }}-react18
+      checkout_paths: packages apps scripts .github
+  react18:
+    name: Build & test with React 18
+    runs-on: ubuntu-latest
+    needs: setup
+    steps:
+      - name: Use "setup" cache
+        id: setup-cache
+        uses: actions/cache@v5
+        with:
+          path: |
+            ./*
+            ~/.pnpm-store
+          key: ${{ github.sha }}-react18
+      - name: Fallback checkout (cache miss)
+        if: steps.setup-cache.outputs.cache-hit != 'true'
+        uses: actions/checkout@v6
+      - name: Install Node.js
+        uses: actions/setup-node@v6
+        with:
+          node-version: '22.12.0'
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+      - name: Fallback install (cache miss)
+        if: steps.setup-cache.outputs.cache-hit != 'true'
+        run: pnpm install
+      - name: Override to React 18
+        run: |
+          pnpm add -Dw react@18 react-dom@18 @types/react@18 @types/react-dom@18
+      - name: Build packages
+        run: pnpm run build
+      - name: Test packages
+        run: pnpm run test
+      - name: Type check packages
+        run: pnpm run types

packages/eds-core-react/package.json

@@ -95,8 +95,8 @@
     "typescript": "^5.9.3"
   },
   "peerDependencies": {
-    "react": "^19",
-    "react-dom": "^19",
+    "react": "^18 || ^19",
+    "react-dom": "^18 || ^19",
     "styled-components": "^6"
   },
   "dependencies": {

packages/eds-data-grid-react/package.json

@@ -31,8 +31,8 @@
   },
   "peerDependencies": {
     "@equinor/eds-core-react": ">=1 <3",
-    "react": "^19",
-    "react-dom": "^19",
+    "react": "^18 || ^19",
+    "react-dom": "^18 || ^19",
     "styled-components": "^6"
   },
   "dependencies": {

packages/eds-lab-react/package.json

@@ -86,8 +86,8 @@
     "typescript": "^5.9.3"
   },
   "peerDependencies": {
-    "react": "^19",
-    "react-dom": "^19",
+    "react": "^18 || ^19",
+    "react-dom": "^18 || ^19",
     "styled-components": "^6"
   },
   "dependencies": {

packages/eds-utils/package.json

@@ -77,8 +77,8 @@
     "@vitejs/plugin-react": "^5.1.4"
   },
   "peerDependencies": {
-    "react": "^19",
-    "react-dom": "^19",
+    "react": "^18 || ^19",
+    "react-dom": "^18 || ^19",
     "styled-components": "^6"
   },
   "dependencies": {