SSH credential host matching fails for git@host format

[javerberg]

Bug Description

When adding an SSH credential with the host format git@bitbucket.org, the credential is not matched when trying to clone a repository. The clone fails with "Permission denied (publickey)".

Steps to Reproduce

1. Go to Settings > Git Credentials
2. Add an SSH credential with host git@bitbucket.org (the pre-filled format when selecting SSH type)
3. Save the credential
4. Try to clone a repo from that host, e.g., git@bitbucket.org:user/repo.git
5. Clone fails with authentication error

Expected Behavior

SSH credential should match and authentication should succeed.

Root Cause

1. Frontend pre-fills git@github.com when selecting SSH type (frontend/src/components/settings/GitCredentialDialog.tsx:180), suggesting this format is valid
2. Backend's getSSHCredentialsForHost (backend/src/utils/git-auth.ts:130) doesn't normalize the git@ prefix
3. When cloning, extractHostFromSSHUrl extracts just bitbucket.org from the repo URL
4. Comparison: git@bitbucket.org ≠ bitbucket.org → no match found