fix(mackup): safer defaults + recovery after broken symlink sync

- Default-off SSR_MACKUP_PRESYMLINK for DynamicProfiles pre-symlink (was
  risking empty/wrong iCloud trees and breaking iTerm2).
- Remove incorrect skip entries: built-in cfgs use different paths than
  ~/.zsh, ~/.vscode*, ~/.iterm2 — skipping hid real overlap from scan only
  but the presymlink change was the main footgun.
- Add `ssr mackup unlink` → `mackup -f link uninstall` to copy configs back
  from Mackup storage and drop symlinks (official undo).
- Docs: ssr.conf.example, README sync/restore wording, completions.

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

config/ssr.conf.example

@@ -16,9 +16,10 @@ SSR_CLOUD_PROVIDER=icloud
 SSR_BACKUP_SUBDIR=BACKUP
 SSR_MACKUP_SUBDIR=Mackup
 
-# Auto-discover uncovered dot-dirs in $HOME and add them to a generated
-# ~/.mackup/ssr-custom.cfg before each backup.  Set to "false" to opt out.
-SSR_MACKUP_AUTODISCOVER=true
+# Optional iTerm2 race workaround: pre-symlink DynamicProfiles → Mackup cloud
+# before `mackup link install`. Default is off — enabling can break iTerm if
+# the cloud copy is incomplete. Prefer `ssr mackup unlink` to recover.
+# SSR_MACKUP_PRESYMLINK=1
 
 # Subdirs (relative to $HOME) to delete before each mackup backup attempt.
 # Handles transient dirs with dangling symlinks or sockets (debug sessions,