Issue 079: Write unit tests for GitHub service operations

[temma02]

Description
Add unit tests for GitHub authentication, repository creation, updates, and push flows.

Requirements and context

• Must be secure, tested, and documented where applicable
• Should stay reviewable and fit the current monorepo structure

Suggested execution

• Create branch: issue-079-write-unit-tests-for-github-service-operations
• Keep changes scoped to the issue and reference the task IDs in the PR

Implement changes

• Mock GitHub REST interactions comprehensively
• Cover permission failures, naming collisions, and retries
• Verify stable error translation

Test and commit

• Run the most relevant tests for the touched service or UI surface
• Include screenshots or request/response examples when the change is user-facing
• Call out edge cases, assumptions, and any follow-up work

Example commit message
test: add github service unit tests

Guidelines

• Prefer small, reviewable PRs
• Keep naming and data contracts consistent with the spec docs
• Preserve responsive and accessible behavior for frontend work