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>

README.md

@@ -2,8 +2,8 @@
 
 Reproducible macOS setup in one command. `ssr` snapshots your Homebrew bundle and application configs to a cloud drive on a schedule, and can rebuild a fresh Mac from that snapshot.
 
-- **Backup** (`ssr sync`): dumps `Brewfile` and runs `mackup backup` to the configured cloud directory.
-- **Restore** (`ssr restore`): installs Homebrew, replays the `Brewfile`, restores `mackup` configs, applies macOS defaults.
+- **Backup** (`ssr sync`): dumps `Brewfile` and runs `mackup link install` to the configured cloud directory (symlink-based).
+- **Restore** (`ssr restore`): installs Homebrew, replays the `Brewfile`, runs `mackup link`, applies macOS defaults.
 - **Scheduled sync**: native macOS `launchd` agent (daily by default).
 - **Cloud storage**: iCloud Drive, Dropbox, Google Drive, OneDrive, or any custom path — selectable via config.
 - **No secrets**: all state lives in your cloud drive; the repo only contains code and config templates.