Fix: Return specific error for no new commits in release analysis

[thomas-vilte]

Description

I updated the AnalyzeNextRelease function in the release service to return a more specific error, ErrNoCommitsSinceLastRelease, when no new commits are detected since the last release. Previously, the function incorrectly returned ErrNoChanges, which suggested a staging issue rather than a lack of new commits for a release. This change improves the clarity of error messages for users.

Fixes #

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

I updated the unit tests for AnalyzeNextRelease in internal/services/release_service_test.go to assert against the new, specific error message.

• Unit tests
• Integration tests
• Manual test: (describe below)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Test Plan & Evidence

Suggested Manual Verification

• API/Backend: Attach JSON response or logs as evidence of correct behavior
• Performance: Ensure no significant latency increase
• Unit Tests: Run go test ./... and ensure all tests pass
• No Regressions: Verify that related features still work as expected