Add offline unit tests for BackupService

[dmccoystephenson]

Summary

Stage B (unit-test expansion) cycle targeting BackupService. No production code is changed.

• testBackupUserRepositories_WithRepositories previously attempted a real clone from https://github.com/testuser/repo1.git; the failure was swallowed, so the test passed without exercising a successful clone. It now clones from a local JGit repository (a file:// URI) and asserts the .git directory was created.
• New testBackupUserRepositories_ExistingRepositoryIsFetched: a second run against an existing backup takes the update path, prints the "updating"/"Updated successfully" lines, and moves refs/remotes/origin/<branch> to the new source commit.
• New testBackupUserRepositories_FailedRepositoryIsSummarizedAndOthersContinue: a repository whose clone fails is listed in the ⚠ Warning: 1 repository(ies) failed to backup: summary while the remaining repository is still cloned.
• New testBackupUserRepositories_BackupDirectoryCannotBeCreated: when the backup directory path is a regular file, the "Failed to create backup directory ''" IOException is raised and no clone is attempted.
• New testGetBackupStatusData_IgnoresFilesAndFormatsLastModified: plain files at either level are not counted, and lastUpdated uses the yyyy-MM-dd HH:mm:ss system-zone format.
• New showBackupStatus tests assert the actual stdout for the missing-directory, empty-directory, and populated cases (previously only assertDoesNotThrow).
• CHANGELOG.md [Unreleased] entry added.

All tests are offline: no network access, filesystem confined to @TempDir, GitHubService/GHRepository mocked, following the existing @Mock + MockitoAnnotations.openMocks(this) pattern. No apparent bugs were surfaced; every assertion characterizes current behavior.

Test plan

• mvn test -Dtest=BackupServiceTest — 16 tests run, 0 failures
• mvn test — 125 tests run, 0 failures, 1 skipped (pre-existing)
• CI Build workflow green on the PR head

Deferred issues

• README links to a LICENSE file that does not exist #8 (README links to a missing LICENSE file) was not picked: adding a license requires a maintainer decision on the copyright holder and year, which cannot be made autonomously.

No tracking issue — gap found during triage (the clone test reached out to github.com, and the status tests asserted nothing about output).

This PR description was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

🤖 Generated with Claude Code

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drafted by Claude on behalf of Daniel Stephenson

[dmccoystephenson]

Self-review rubric (head CI: build pass, docker-build pass):

• Scope: PASS — only src/test/java/com/github/backup/BackupServiceTest.java and one CHANGELOG.md line are modified; no production code touched.
• Tests-new: PASS (N/A) — no new public methods are introduced; the new private helpers (createSourceRepository, commitFile, captureStdout) are exercised by every test that uses them.
• Tests-fix: N/A — no bug fix in this PR; all assertions characterize current behavior, and none of them exposed a defect.
• Sibling structure: PASS — follows the test<MethodName>_<Scenario> naming, @Mock + MockitoAnnotations.openMocks(this), and @TempDir conventions already used in the file.
• Sibling renames: N/A — nothing renamed.
• Docs: PASS — no CLI flag, property, or endpoint changes; CHANGELOG.md [Unreleased] records the test addition in the same style as the Add offline unit tests for GitHubService.getPublicRepositories #29 entry.
• Issue resolution: N/A — no Closes #N; the gap was found during triage, and README links to a LICENSE file that does not exist #8's deferral reason is recorded in the PR body.
• CI: PASS — both jobs green on the head SHA; locally mvn test ran 125 tests, 0 failures, 1 pre-existing skip.
• Config-doc parity / Command-doc parity: N/A — no configuration or command surface changed.
• Package placement: PASS — the test stays in the 1:1 mirror location.
• No credential leakage: PASS — no tokens used; the tests no longer contact github.com at all.

Observations (no change applied):

• src/test/java/com/github/backup/BackupServiceTest.java (testBackupUserRepositories_FailedRepositoryIsSummarizedAndOthersContinue) — the failure is triggered by a file:// URI that does not exist, which relies on JGit raising on a missing source. A JGit upgrade that changed this to a silent empty clone would make this test fail loudly, not pass silently, so it is acceptable as a regression guard.
• captureStdout swaps System.out globally; Surefire runs test classes sequentially in this build (no parallel config in pom.xml), so the swap cannot interleave with another class's output.

Summary: test-only change that removes the last live network call from BackupServiceTest and turns three assertDoesNotThrow-only tests into output assertions.

This review comment was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

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drafted by Claude on behalf of Daniel Stephenson