ci: move workflows from Node 20 (EOL) to Node 24 LTS

[Ndevu12]

Moves all CI/CD jobs off an end-of-life Node runtime, and unblocks #95 as a consequence.

Node 20 is EOL

Node 20 reached end-of-life on 2026-04-30. Every job in this repo — CI, Pages deploy, and release — has been running on a runtime that no longer receives security patches. All six node-version pins across ci.yml, deploy.yml, and release.yml move to Node 24, the current LTS (supported to April 2028).

This is also the real fix for #95

#95 (jsdom 29 → 30) fails CI, and the reported error is misleading:

ERROR: Coverage for lines (0%) does not meet global threshold (80%)

That is a symptom, not the cause. The actual failure is that every vitest worker crashed before running a single test:

Error: [vitest-pool]: Failed to start forks worker for test files .../Dialogs.test.tsx
  at Object.<anonymous> node_modules/jsdom/lib/api.js:12:33

jsdom@30 requires Node ^22.22.2 || ^24.15.0 || >=26.0.0. On Node 20 it cannot load at all, so no test executed, so coverage was 0%, so the 80/75 thresholds failed.

The tempting quick fixes here are both wrong:

• Pinning jsdom back to 29 hides the fact that CI runs an EOL runtime.
• Lowering the coverage thresholds would mask a total test-execution failure as if it were a coverage regression. Actual coverage on main is healthy at 92.9% statements / 84.1% branches — the thresholds are correct and should not be touched.

Raising Node fixes the underlying condition, after which #95 can merge on its own merits.

Deliberately not adding an engines field

This is a browser-targeted library; Node is only a build and test concern. Declaring a Node floor in package.json would constrain consumers without benefiting them.

Verification

CI on this PR is itself the test — every job now runs on Node 24. Once green, I will rebase #95 onto this and confirm the jsdom 30 suite passes.