Add the dsh-workspace-changes Host plugin that snapshots the working tree at
turn start and end through a private git index, diffs the two trees, folds in
file-tool hunks for ignored and out-of-tree files, and appends a log-only
workspace/changes event. The Web deliverables plugin renders that event as the
changed-files card in place of the mutation-call row, with default-app and
common-folder opening through a new authenticated route.