chore: improve api error messages (CM-855)

[joanagmaia]

Changes

Repositories already mapped to other projects

• For GitHub, GitLab, Gerrit and Git throw 400 with a meaningful message if user is trying to connect to a repository that is already connected to another integration:
  • Backend Message: Trying to update gitlab repo ${row.url} mapping with integrationId ${integrationId} but it is already mapped to integration ${row.integrationId}!
  • Frontend is already handling this message for github but it's missing to handle it the same way for github-nango, gerrit and git. This logic should be refactored and reused for the remaining code integrations -> https://github.com/CrowdDotDev/crowd.dev/blob/chore/improve-api-error-messages/frontend/src/config/integrations/github/components/settings/github-settings-drawer.vue#L354
    • Frontend message: The repository {repo url} is already connected with project {Project name}

Creating segments with names or slugs that already exist

• If slug or name already exist in another project, throw a meaningful error.
  • Backend Message:
    • subprojectSlugExists: Sub-project with slug "{0}" already exists in project {1}.,
    • projectSlugExists: Project with slug "{0}" already exists in project group {1}.,
    • projectGroupSlugExists: Project Group with slug "{0}" already exists.,
    • subprojectNameExists: Sub-project {0} already exists in project {1}.,
    • projectNameExists: Project {0} already exists in project group {1}.,
    • projectGroupNameExists: Project Group {0} already exists.
  • Frontend should render exactly what it receives from backend (for segments (all levels) creation and update)

---

Note

Adds checks to prevent mapping the same repo to multiple integrations and introduces centralized validation for duplicate segment names/slugs with specific error messages.

• Integrations (Git/GitHub/GitLab):
  • Enforce repo mapping uniqueness: before updating mappings, check existing records and throw Error400('errors.integrations.repoAlreadyMapped', ...) if a repo is already linked to another integrationId.
  • Standardize error key/message to errors.integrations.repoAlreadyMapped.
• Segments:
  • Add centralized conflict validation for name/slug across levels (project group/project/sub-project), including LF vs non-LF slug variants; used on create and update.
  • New helpers: validateSegmentConflicts, throwSegmentConflictError, validateUpdateDuplicates, getSegmentType; repository method findByName.
• i18n:
  • Add granular segment conflict messages and unify repo-mapped error wording.

^{Written by Cursor Bugbot for commit 9ff86dd. This will update automatically on new commits. Configure here.}

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[cursor]

Bug: Update validation misses slug conflicts from isLF transformation

When updating a segment, validateUpdateDuplicates skips slug validation if data.slug === segment.slug (line 735). However, the slug is subsequently transformed by validateNonLfSlug when isLF changes to false (line 54). The transformed slug (with nonlf_ prefix) is never validated for conflicts. This allows creating duplicate slugs when a user updates a segment with the same slug value but changes isLF from true to false, potentially colliding with an existing segment that already has the nonlf_-prefixed version of that slug.

Additional Locations (1)

• backend/src/services/segmentService.ts#L733-L735