docs(CONTRIBUTING): update stale sbx-kits/ path to acq-kits/ #255

Summary

CONTRIBUTING.md (lines ~96 and ~99) still points at integrations/isolation/sbx-kits/ in the GSA-TTS/agentic-coding-patterns repo:

the sbx kits it applies — and their tests (permission-matrix, model-sync, per-kit scripts/verify) … live in the … repo under integrations/isolation/sbx-kits/.

The patterns repo's canonical kit tree is now integrations/isolation/acq-kits/ (the neutral, both-backend kits the acq wrapper applies). sbx-kits/ still exists but is the older/legacy layout. AGENTS.md was updated to acq-kits/ in the msb-parity work (GSA-TTS/agentic-coding-quickstart#233); CONTRIBUTING.md should match.

Fix

• Update the two sbx-kits/ references in CONTRIBUTING.md to acq-kits/.
• Reword "the sbx kits it applies" → "the kits it applies" (they apply to both SBX and MSB now).
• While there, sanity-check the surrounding paragraph for other sbx-only phrasing that should be backend-neutral.

Context

Found during the AGENTS.md sbx→(sbx/msb) generalization on feat/msb-parity. Out of scope for that PR (which is msb-parity, not CONTRIBUTING), filed per the discovered-defect tracking rule. Docs-only, low risk.

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