Add top-level `mosaic uninstall` with --framework, --cli, --gateway, --all,
--keep-data, --yes, and --dry-run flags. Implements runtime asset reversal
(backup restore or managed-copy removal), npmrc scope line removal, and
gateway delegation. Adds install manifest (write on install, read on uninstall)
for precise reversal; falls back to heuristic mode when manifest is absent.
Shell fallback via `tools/install.sh --uninstall`. Closes#425.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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