Refactor internal packages and fix git add for staged deletions

[thomas-vilte]

Description

I have reorganized several internal packages to improve the project's structure and simplify import paths. Specifically, the cost and routing related services have been moved from internal/services/cost and internal/services/routing to internal/cost and internal/routing respectively. Additionally, the CleanLabels helper function has been moved from internal/ai/gemini/helpers.go to internal/ai/gemini/helper.go.

I also addressed a bug in the git_service where calling AddFileToStaging on a file that was already staged for deletion would result in an error ("pathspec did not match any files"). The service now correctly handles this scenario as a no-op, preventing unnecessary failures.

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?

• Unit tests
• Integration tests
• Manual test: The fix for handling already staged deleted files includes a dedicated unit test case (TestAddFileToStaging/Already_fully_staged_deleted_file_is_a_no-op) that reproduces the original failure and verifies the corrected behavior. Existing unit tests for the refactored packages were updated to reflect the new import paths and continue to pass.

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