Add baseline GitHub Actions CI checks

[Andresshamis]

Meridian PR Agent automation, posting through @Andresshamis.

Summary

Adds the first repository-level GitHub Actions CI workflow for Meridian's current SwiftPM-safe verification path.

Linked issue: Closes #41
Base branch: dev
Branch: ci/baseline-github-actions

What Changed

• Added .github/workflows/ci.yml for pull requests targeting dev/main and pushes to dev/main.
• Runs on macos-26, prints Swift/Xcode runner versions, then runs swift build, swift test, bash -n script/build_and_run.sh, and diff whitespace checks.
• Uses actions/checkout@v6 to avoid the Node 20 checkout deprecation warning seen on the first CI attempt.
• Documents the baseline CI check in README.md, Docs/TestPlan.md, and Docs/ReleaseChecklist.md.

Why It Changed

Open PRs previously had empty status check rollups, so PR Agent and Reviewer coordination depended only on local command reports. This provides a machine-readable baseline gate for build, tests, script syntax, and whitespace hygiene.

Security Considerations

The workflow uses permissions: contents: read and does not require Apple signing secrets, cookies, tokens, private keys, browsing data, or private browsing data. Signed UI tests, notarization, and release signing remain out of scope until a signing-capable owner-approved setup exists.

Testing Performed

• ruby -e 'require "psych"; Psych.parse_file(".github/workflows/ci.yml")'
• bash -n script/build_and_run.sh
• git diff --check
• swift test (117 tests)
• swift build
• git diff --cached --check
• GitHub Actions CI / SwiftPM baseline passed on run Bootstrap native macOS browser shell #2 for head b4954b2.

Known Limitations

• This first CI slice intentionally excludes signed app launch, UI smoke tests, notarization, and branch protection.

Follow-Up Work

• Add signed Xcode app/UI smoke checks after issue Add Xcode app project and UI test host #4 / PR Add Xcode app project and UI test host #12 provides a usable app/UI test host and Andres approves any required CI signing credentials.
• Consider branch protection after the baseline workflow is proven stable.

Screenshots / Recordings

Not applicable; this is CI and documentation only.

[Andresshamis]

Meridian PR Agent automation, posting through @Andresshamis.

Status: ready for review.

The baseline CI workflow is now visible on this PR and passed on head b4954b2.

Checks completed:

• Local YAML parse for .github/workflows/ci.yml
• bash -n script/build_and_run.sh
• git diff --check
• swift test (117 tests)
• swift build
• git diff --cached --check
• GitHub Actions CI / SwiftPM baseline run Bootstrap native macOS browser shell #2: passed

Note: the first Actions run passed but warned about actions/checkout@v4 using Node 20, so I pushed a follow-up commit switching the workflow to actions/checkout@v6. The passing run above is the updated workflow.

[Andresshamis]

Meridian Reviewer automation, posting through @Andresshamis.

Review conclusion: ready and merging

Findings:

• None.

Tests/checks run:

• ruby -e 'require "psych"; Psych.parse_file(".github/workflows/ci.yml")': passed.
• bash -n script/build_and_run.sh: passed.
• git diff --check origin/dev...HEAD: passed.
• swift build: passed.
• swift test: passed, 117 tests.
• GitHub Actions CI / SwiftPM baseline: passed on head b4954b2.

Follow-up issues:

• None created. Existing follow-up for signed app/UI host remains Add Xcode app project and UI test host #4 / PR Add Xcode app project and UI test host #12, and branch protection can wait until this baseline proves stable.

Stack/merge state:

• PR Add baseline GitHub Actions CI checks #44 targets dev, is not stacked, is mergeable, and has passing CI.

Decision:

• Merging into dev with no blockers. Formal approval was unavailable because GitHub does not allow this owner account to approve its own PR.

Open questions:

• None.

Summary:

• The workflow is appropriately scoped for the current SwiftPM-safe baseline, uses read-only repository permissions, documents its limitations, and improves Reviewer/PR Agent coordination without introducing signing or secret exposure.