feat: plan-01 Phase 0 — restructure skeleton (packages/casan-harness + apps/okr/domain)

Empty package/app skeleton for the harness restructure. No harness files moved yet; full gate baseline stays PASS=64 FAIL=0 SKIP=3. Subdirs materialize via git mv in Phases 1-5.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

AINative_OKR_CASAN5/apps/okr/domain/README.md

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+# apps/okr/domain (skeleton)
+
+OKR-domain data consumed by the CASAN harness, kept separate from the reusable harness package.
+Populated in Plan-01 Phase 5. Referenced by scripts via `CASAN_DOMAIN_ROOT` (default this dir).
+
+Planned contents (moved from `.specify/` / `docs/` in Phase 5):
+- `golden-runs/` — golden baselines for drift/H7 (from `.specify/level5/golden-runs/`)
+- `input/` — requirement/architecture specs (from `docs/input/`)
+- `corpus/` — redteam + benign corpora (from `.specify/security/redteam-*.jsonl`, `benign-corpus/`)