test: cover ghost member commits and issue reclose mapping (CM-1473)

[mbani01]

Problem

The fixes merged in #4776 (ghost-author PR commits) and #4777 (latest issue close event) shipped without their unit tests committed.

Change

Adds the Vitest coverage written alongside those fixes:

• pullRequestCommits.test.ts: a commit whose author has no GitHub account is emitted as the ghost member (plus harness support for capturing emits)
• mappers/issue.test.ts: a reopened-then-reclosed issue emits the latest close event's timestamp; an open issue emits no close activity

Validation

• npx vitest run on both files against main: 6/6 pass
• oxfmt --check + oxlint --deny-warnings: clean

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Test-only changes that document existing behavior; no runtime or deployment impact.

Overview
Adds Vitest coverage that was missing after earlier GitHub connector fixes (CM-1473), with no production code changes.

Introduces mappers/issue.test.ts to lock in toIssueActivities behavior: a closed issue with a timeline close event gets an issue-closed activity with the latest timestamp and closedBy; an open issue does not emit a close activity.

Extends pullRequestCommits.test.ts so the sync harness records emitted activities and can simulate commits with author.user = null, plus a new case asserting those commits map to the ghost member identity.

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[Copilot]

Copilot review overview

🟡 Changes recommended

The issue fixtures do not exercise the query regression or the open-state guard they claim to protect.

Get a fresh assessment by requesting another Copilot review.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• Test does not verify requesting the latest close event · New
• Remove redundant ghostAuthorPrs comment · New

What changed in this PR

Adds missing regression tests for GitHub connector behavior around ghost commit authors and issue closure events.

Changes:

• Captures emitted commit activities and verifies ghost-member mapping.
• Adds issue close-event mapper scenarios.

File	Description
syncs/​pullRequestCommits.test.ts	Tests commits without resolvable GitHub users.
mappers/​issue.test.ts	Tests closed and currently open issue mapping.

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[Copilot]

Copilot review overview

🟡 Changes recommended

The issue test does not exercise the query behavior responsible for selecting the latest close event.

Get a fresh assessment by requesting another Copilot review.

Review effort: Balanced
Findings: 1 · 2

Open (3)

• Test does not verify requesting the latest close event
• Capitalize GitHub in test description · New
• Remove redundant ghostAuthorPrs comment