SDK-613: make the build matrix fail the run, and swap node 21 for 24

Addresses both review comments on the CI workflow.

`continue-on-error: true` sat on the `build` job, so every matrix leg
could fail while the run still reported success -- the reason the
`npm ci` breakage in this branch showed up as a green run. Removed it,
so a regression in `Lint`, `Build`, `Test` or the new `Test examples`
step now fails CI. `strategy.fail-fast: false` takes its place, which
is what the original setting was presumably reaching for: every runtime
still reports instead of being cancelled by the first failure.

Node 21 has been end-of-life since June 2024, so that slot becomes node
24 (paired with npm 11, the version it bundles). The matrix is now node
20 -- the floor Next.js 16 supports, and what the examples pin -- plus
the two maintained LTS lines, 22 and 24.

Verified: the full CI sequence (`install:all -- ci`, `lint`,
`lint:examples`, `build:all` across all four examples, `test`,
`test:examples`) passes locally on node 24.21.0 with npm 11, as it
already does on 22.23.2 with npm 10.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: AI Agent

.github/workflows/ci.yaml

@@ -13,17 +13,19 @@ jobs:
     runs-on: ubuntu-latest
 
     strategy:
+      # Let every runtime report rather than cancelling its siblings on the
+      # first failure -- but the job itself must still fail the run.
+      fail-fast: false
       matrix:
         include:
-          # Next.js 16 (used by the examples) requires node >= 20.9.
+          # Next.js 16 (used by the examples) requires node >= 20.9, so 20 is
+          # the floor. 22 and 24 are the maintained LTS lines.
           - node: 20
             npm: 10
-          - node: 21
-            npm: 10
           - node: 22
             npm: 10
-
-    continue-on-error: true
+          - node: 24
+            npm: 11
 
     steps:
       - name: Checkout