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>

bin/ssr

@@ -27,14 +27,14 @@ Usage:
 
 Commands:
   install              First-time install: links binary, seeds config, schedules sync.
-  sync                 Run a backup: brew bundle dump + mackup backup → cloud.
-  restore [Brewfile]   Restore a machine: brew bundle + mackup restore + macOS defaults.
+  sync                 Run a backup: brew bundle dump + mackup link install → cloud.
+  restore [Brewfile]   Restore a machine: brew bundle + mackup link + macOS defaults.
   update [--dry-run]   Pull latest ssr code, refresh launchd if needed.
   schedule on|off      Enable/disable the scheduled launchd sync job.
   config show|edit     Print or edit the active config file.
   completions          Install or remove shell completions (zsh/bash/fish).
   status               Show last sync time, cloud target, and scheduled state.
-  mackup scan|list|clean  Manage auto-generated Mackup app definitions.
+  mackup scan|list|clean|unlink  Mackup ssr-*.cfg helpers + symlink revert.
   version              Print version.
 
 Options: