The initial fix only checked loadWorkspaceConfig, but the dashboard
POST /api/projects and `fn project add` routes never create workspace.json
(only registerProjectInteractive does). So re-adding a workspace project
through the dashboard still triggered git init because the guard saw no
workspace.json.
Add detectWorkspaceRepos as a fallback: after loadWorkspaceConfig and
isInsideGitWorkTree both miss, probe for git sub-repos. If found, persist
workspace.json and return 'existing' without running git init. This covers
all registration surfaces.