fix(server): handle offline team reviewer sync gracefully

[mertilginoglu]

Motivation

Issue #860 reports repeated server error logs when team reviewer expansion runs while the GitHub client is offline. These logs are noisy and misleading because offline mode can
be an expected runtime state.

Description

Updated pull request sync logic to treat offline reviewer-team expansion failures as expected behavior instead of hard errors.

Changes:

• In GitHubPullRequestSyncService, added isOfflineError(IOException) to classify offline errors.
• For offline reviewer expansion failures, log at DEBUG and continue sync.
• Kept ERROR logging for non-offline failures.
• Added unit tests for offline error classification in GitHubPullRequestSyncServiceTest.

Testing Instructions

Prerequisites:

• Java 21
• Gradle wrapper available (./gradlew)
• Checked out branch fix/860-offline-reviewer-sync

Flow:

1. Run:
   ./gradlew :application-server:test --tests de.tum.cit.aet.helios.pullrequest.github.GitHubPullRequestSyncServiceTest
2. Verify tests pass.
3. Optionally run:
   ./gradlew :application-server:test --tests de.tum.cit.aet.helios.branch.github.GitHubBranchComparisonServiceTest
4. Inspect GitHubPullRequestSyncService and confirm offline cases are handled via debug logging while other IO failures remain error-level.

Screenshots

No UI changes were made.

Checklist

General

• PR description explains the purpose and changes. (f.e. following the 'Conventional Commits') (https://www.conventionalcommits.org/en/v1.0.0/)
• Changes have been tested locally.

Server

• Code is performant and follows best practices

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.21% (target: -1.00%)	✅ 14.29%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (73b4871)	7927	2126	26.82%
Head commit (62b7766)	7991 (+64)	2160 (+34)	27.03% (+0.21%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#883)	14	2	14.29%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[github-actions]

There hasn't been any activity on this pull request recently. Therefore, this pull request has been automatically marked as stale and will be closed if no further activity occurs within seven days. Thank you for your contributions.