Use organization workflows for CI, release and pages deployment

[db9795]

CI and release now call the shared workflows from maptoolkit/.github instead of defining the steps here.

• ci.yml: calls npm-ci.yml@main (lint, typecheck, test, build — same steps as before). Push runs are limited to main, PRs run as before. The old if that skipped same-repo PRs to avoid duplicate runs is no longer needed.
• release.yml: calls npm-release.yml@main (changesets release PR / npm publish, tags and GitHub releases — same steps as before). A new deploy-pages job runs after it when the release output published is 'true'.
• deploy_pages.yaml → deploy-pages.yml: triggered via workflow_call from the release workflow (and still manually via workflow_dispatch) instead of on v* tag pushes. Tags pushed with GITHUB_TOKEN don't trigger other workflows, so the demo was never deployed automatically after a release. The unused VITE_MAPTOOLKIT_API_KEY env is removed, the demo uses demo/example.geojson.

The shared workflows use actions/checkout and actions/setup-node v6 and pin changesets/action to v1.9.0.