Arcane is an interface for managing Docker containers, images, networks, and volumes. Prior to 1.19.0, Arcane's huma-based REST API exposes nine endpoints under /api/customize/git-repositories and /api/git-repositories/sync for managing GitOps source repositories and their stored credentials. Eight of those endpoints (list, create, get, update, delete, test, listBranches, browseFiles) never call the checkAdmin(ctx) helper that every other admin-managed resource (container registries, environments, users, API keys, swarm, settings, system, notifications, events) uses, and the huma authentication middleware deliberately enforces only authentication, not the admin role. As a result, any logged-in user with the default user role can list, create, modify, delete, and test git repository configurations. By repointing an existing repository's URL to an attacker-controlled host while omitting the token/sshKey fields (which UpdateRepository only rewrites when explicitly supplied), the attacker causes Arcane to decrypt the legitimate PAT/SSH key on its next /test, /branches, or /files call and present it as HTTP Basic auth (or SSH key auth) to the attacker's host — producing a one-step exfiltration of plaintext Git credentials. This vulnerability is fixed in 1.19.0.

Affected: Go: github.com/getarcaneapp/arcane/backend

## Summary

Arcane's huma-based REST API exposes nine endpoints under `/api/customize/git-repositories` and `/api/git-repositories/sync` for managing GitOps source repositories and their stored credentials. Eight of those endpoints (`list`, `create`, `get`, `update`, `delete`, `test`, `listBranches`, `browseFiles`) never call the `checkAdmin(ctx)` helper that every other admin-managed resource (container registries, environments, users, API keys, swarm, settings, system, notifications, events) uses, and the huma authentication middleware deliberately enforces only authentication, not the `admin` role. As a result, any logged-in user with the default `user` role can list, create, modify, delete, and test git repository configurations. By repointing an existing repository's URL to an attacker-controlled host while omitting the `token`/`sshKey` fields (which `UpdateRepository` only rewrites when explicitly supplied), the attacker causes Arcane to decrypt the legitimate PAT/SSH key on its next `/test`, `/branches`, or `/files` call and present it as HTTP Basic auth (or SSH key auth) to the attacker's host — producing a one-step exfiltration of plaintext Git credentials.

## Details

### Auth bridge does not enforce role

`backend/internal/huma/middleware/auth.go:192-254` (`NewAuthBridge`) validates Bearer JWTs / API keys / agent tokens and stores the user (and an `userIsAdmin` flag) in the request context, but it never rejects non-admin callers — admin enforcement is intentional…