fix: back up Docker Desktop config files only, not the whole ~/.docker dir

Docker Desktop checks that ~/.docker is a real directory and rejects it
if it is a symlink (Mackup's default when backing up a whole dir).

Solution: remove .docker from the skip list, add it to curated + selective.
Mackup will symlink only ~/.docker/config.json and ~/.docker/daemon.json —
the directory itself stays a real dir that Docker Desktop can manage.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/mackup.sh

@@ -17,6 +17,7 @@ _SSR_MACKUP_CURATED=(
     .codex           # OpenAI Codex config
     .easymcp         # EasyMCP config
     .factory         # Factory AI config
+    .docker          # Docker Desktop — selective files only (see _SSR_MACKUP_SELECTIVE)
     .config/claude
     .config/cursor
     .config/gh       # GitHub CLI (if not already in mackup)
@@ -39,6 +40,9 @@ _SSR_MACKUP_SELECTIVE=(
     ".vscode=settings.json,keybindings.json,snippets"
     ".vscode-insiders=settings.json,keybindings.json,snippets"
     ".factory=settings.json,droids"
+    # Docker Desktop rejects ~/.docker as a symlink — back up individual files
+    # only so ~/.docker/ stays a real directory that Docker Desktop can manage.
+    ".docker=config.json,daemon.json"
 )
 
 # Dot-dirs/files to never auto-include.
@@ -47,7 +51,10 @@ _SSR_MACKUP_SKIP=(
     .Trash .localized .DS_Store .CFUserTextEncoding
     .cache .npm .yarn .pnpm .bun
     .gradle .m2 .ivy2 .sbt
-    .docker .vagrant .minikube .kube .helm
+    # .docker is handled via _SSR_MACKUP_SELECTIVE (individual files only).
+    # Docker Desktop rejects ~/.docker being a symlink, so we never back up
+    # the whole directory — only config.json / daemon.json as file symlinks.
+    .vagrant .minikube .kube .helm
     .local          # runtime state, not config
     .bash_history .zsh_history .zsh_sessions .sh_history
     .lesshst .wget-hsts .python_history .node_repl_history