Lands the dispatch entry point for the Nomad+Vault migration. The docker
path remains the default and is byte-for-byte unchanged. The new
`--backend=nomad` value routes to a `_disinto_init_nomad` stub that fails
loud (exit 99) so no silent misrouting can happen while S0.2–S0.5 fill in
the real implementation. With `--dry-run --backend=nomad` the stub reports
status and exits 0 so dry-run callers (P7) don't see a hard failure.
- New `--backend <value>` flag (accepts `docker` | `nomad`); supports
both `--backend nomad` and `--backend=nomad` forms.
- Invalid backend values are rejected with a clear error.
- `_disinto_init_nomad` lives next to `disinto_init` so future S0.x
issues only need to fill in this function — flag parsing and dispatch
stay frozen.
- `--help` lists the flag and both values.
- `shellcheck bin/disinto` introduces no new findings beyond the
pre-existing baseline.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
