ci: add ci-website workflow for twenty-website-new (#20281)

## Summary
- Recreates the `ci-website.yaml` workflow that was removed alongside
`twenty-website` in #20270, now scoped to `twenty-website-new`.
- Replaces the old build-only job with a `[lint, typecheck, test]`
matrix run via `./.github/actions/nx-affected` on `tag:scope:website` —
same idiom used by `ci-shared.yaml`.
- Path filter watches `packages/twenty-website-new/**` and
`packages/twenty-shared/**` (since website-new depends on
`twenty-shared`), plus `package.json` / `yarn.lock`.

## Test plan
- [ ] CI Website workflow appears on this PR and the `lint`,
`typecheck`, `test` matrix jobs all pass
- [ ] `ci-website-status-check` is green

.github/workflows/ci-website.yaml

@@ -0,0 +1,58 @@
+name: CI Website
+
+on:
+  pull_request:
+  merge_group:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
+
+jobs:
+  changed-files-check:
+    if: github.event_name != 'merge_group'
+    uses: ./.github/workflows/changed-files.yaml
+    with:
+      files: |
+        package.json
+        yarn.lock
+        packages/twenty-website-new/**
+        packages/twenty-shared/**
+  website-task:
+    needs: changed-files-check
+    if: needs.changed-files-check.outputs.any_changed == 'true'
+    timeout-minutes: 30
+    runs-on: ubuntu-latest
+    env:
+      NODE_OPTIONS: '--max-old-space-size=6144'
+    strategy:
+      matrix:
+        task: [lint, typecheck, test]
+    steps:
+      - name: Cancel Previous Runs
+        uses: styfle/cancel-workflow-action@0.11.0
+        with:
+          access_token: ${{ github.token }}
+      - name: Fetch custom Github Actions and base branch history
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 10
+      - name: Install dependencies
+        uses: ./.github/actions/yarn-install
+      - name: Run ${{ matrix.task }} task
+        uses: ./.github/actions/nx-affected
+        with:
+          tag: scope:website
+          tasks: ${{ matrix.task }}
+  ci-website-status-check:
+    if: always() && !cancelled()
+    timeout-minutes: 5
+    runs-on: ubuntu-latest
+    needs: [changed-files-check, website-task]
+    steps:
+      - name: Fail job if any needs failed
+        if: contains(needs.*.result, 'failure')
+        run: exit 1