Upgrade Node.js from 20 to 22 LTS

Node 20 LTS reaches end-of-life April 2026. Updated all references:
- Dockerfile base image to node:22
- All GitHub Actions workflows to Node 22
- Bumped actions/checkout and actions/setup-node to v4 where outdated
- Added .nvmrc file for local development

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/build-frontend.yml

@@ -13,13 +13,13 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [20.x]
+        node-version: [22.x]
         # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Use Node.js ${{ matrix.node-version }}
-      uses: actions/setup-node@v3
+      uses: actions/setup-node@v4
       with:
         node-version: ${{ matrix.node-version }}
         cache: 'npm'

.github/workflows/deploy.yml

@@ -19,7 +19,7 @@ jobs:
     - name: Setup Node.js
       uses: actions/setup-node@v4
       with:
-        node-version: '20'
+        node-version: '22'
 
     - name: Install dependencies
       run: npm ci

.github/workflows/fix-code-styles.yml

@@ -12,10 +12,10 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
-    - uses: actions/setup-node@v3
+    - uses: actions/checkout@v4
+    - uses: actions/setup-node@v4
       with:
-        node-version: 20
+        node-version: 22
         cache: 'npm'
     - run: npm ci
     - run: npm run lint-fix

.github/workflows/update-query-hashes.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Setup Node.js
       uses: actions/setup-node@v4
       with:
-        node-version: '20'
+        node-version: '22'
 
     - name: Install dependencies
       run: npm ci

.nvmrc

@@ -0,0 +1 @@
+22

docker/app/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:20
+FROM node:22
 
 # App setup
 WORKDIR /app