feat: Node.js 24 and 26 images; refuse builds below the Oct 2026 security floor

- One install-node.sh <major> replaces install-node{18,20,22}.sh. It fails the
  build if NodeSource hands back a version below the newest security release
  for the line (22.23.4 / 24.22.1 / 26.12.1: CVE-2026-111497 Brotli OOB write
  and 9 others), so a lagging mirror can't ship a vulnerable image silently.
  18 and 20 are EOL: they still build, with a warning.
- CI matrix adds 24 and 26; fail-fast off so one line can't cancel the rest.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/build-push.yaml

@@ -9,8 +9,9 @@ jobs:
   Build-and-Push:
     runs-on: ubuntu-latest
     strategy:
+      fail-fast: false
       matrix:
-        nodever: [18, 20, 22]
+        nodever: [18, 20, 22, 24, 26]
     steps:
       - name: Checkout
         uses: actions/checkout@v4