acq: intercept --kit <ref> on run/create and translate it (currently passed raw to the backend, breaking neutral kits) #222

Summary

acq run/acq create do not intercept a user-supplied --kit <path> flag.
The flag falls through to the backend (acq_backend_provision only strips
--name), so it reaches sbx create --kit <path> untranslated. Since a
neutral hybrid/v1 kit is a different schema than sbx-v2, sbx rejects it:

$ acq run opencode --kit ../agentic-coding-patterns/integrations/isolation/acq-kits/openchamber .
ERROR: resolve kits: kit "...": artifact: invalid spec.yaml: yaml: unmarshal errors:
  line NN: field files not found in type spec.SpecFile
  line NN: cannot unmarshal !!seq into spec.CommandsPolicy
  line NN: field backend_extras not found in type spec.SpecFile

Expected

--kit <ref> (repeatable) on acq run / acq create should be treated like an
entry in ACQ_EXTRA_KITS: added to the kit list so it goes through the neutral→
backend translation (_acq_sbx_translate_kit for sbx), and not forwarded to
the backend CLI as a raw flag.

Workaround (today)

Pass the kit via the env var, which IS translated:

ACQ_EXTRA_KITS="/abs/path/to/kit" acq run opencode .

Notes / scope

• --kit is a natural, discoverable way to apply a local kit; users reach for it
  before finding ACQ_EXTRA_KITS (it's also how the sbx backend spells it).
• Both run and create should honor it; both backends (sbx, msb) already build
  their kit list from the same ACQ_EXTRA_KITS seam, so folding --kit into that
  list makes it backend-agnostic.
• Kit-source allowlisting (kit.allowedSources) should apply to --kit refs the
  same way it does to ACQ_EXTRA_KITS.
• Related: acq(kit-translate): backend_extras.sbx.publishedPorts is dropped in neutral→sbx translation #219, acq(kit-translate): caps.network.allow entries emitted unquoted — wildcard host (e.g. *.npmjs.org) yields invalid sbx spec #220 (both fixed in fix(acq): carry publishedPorts and quote allow hosts in kit-translate #221) were other kit-translate gaps found in
  the same investigation.