ci: trigger selfpatch_demos CI on push to main

[bburda]

Pull Request

Summary

Adds a notify-demos job to the CI workflow that dispatches a repository_dispatch event to selfpatch/selfpatch_demos after both jazzy-lint and jazzy-test pass on pushes to main. This keeps the integration demo suite in sync with every gateway merge.

• Fires only on push to main (skipped on PRs via the if: condition)
• Waits for jazzy-lint and jazzy-test to both succeed before dispatching
• Sends client-payload with sha and run_url so the selfpatch_demos job summary can link back to the triggering gateway CI run
• Uses peter-evans/repository-dispatch@v4 with the DEMOS_DISPATCH_TOKEN secret (fine-grained PAT with contents:write on selfpatch/selfpatch_demos)

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Issue

• closes Trigger selfpatch_demos CI on merge to main #224

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Type

• Bug fix
• New feature or tests
• Breaking change
• Documentation only

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Testing

The notify-demos job will be skipped on this PR (the if: condition evaluates to false for pull_request events). End-to-end validation will happen after both this PR and selfpatch/selfpatch_demos#36 are merged: the next push to main will dispatch ros2_medkit_updated to selfpatch_demos and trigger its CI.

Pre-conditions:

• DEMOS_DISPATCH_TOKEN secret is already configured in this repo (confirmed via gh secret list)
• ci: trigger builds on ros2_medkit_updated dispatch selfpatch_demos#36 (which registers the ros2_medkit_updated trigger on the selfpatch_demos side) must be merged before this PR lands

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Checklist

• Breaking changes are clearly described (and announced in docs / changelog if needed)
• Tests were added or updated if needed
• Docs were updated if behavior or public API changed

[Copilot]

Pull request overview

Adds a downstream CI trigger so that every successful merge to main in ros2_medkit can automatically kick off the integration demo suite in selfpatch/selfpatch_demos, keeping demo Docker builds synchronized with gateway changes.

Changes:

• Adds a new notify-demos GitHub Actions job gated to push events on main.
• Configures notify-demos to wait for jazzy-lint and jazzy-test success before dispatching ros2_medkit_updated via repository_dispatch.
• Includes sha and run_url in client-payload for traceability back to the triggering workflow run.