feat(mvp): working secrets-engine CLI for the whynot-design npm publish lane

Implements SECRETS-WP-0002 end to end as a uv-managed Python package:

- catalog: non-secret lane registry + strict validator (build/test/prod)
- stage roles + OpenBao ACL policies; guards refuse wildcards, sys/, identity/,
  admin names, and cross-stage paths before any backend call
- plan/apply: dry-run-first, idempotent policy + approle apply, decision-gated
- decisions: State Hub lookup with local-fixture fallback; non-secret evidence
  to JSONL + hub progress, scrubbed of any value
- provision/verify: mode-0600 file import + generated test values; positive/
  negative checks that never print the value
- exec delivery: `exec --catalog ... -- npm publish` injects the token via a
  temp .npmrc for the child only, cleaned up on exit/failure/interrupt
- ops-warden routing contract + hardening backlog docs
- 34 tests incl. live OpenBao integration; scripts/demo-e2e.sh runs the full
  chain against a throwaway bao dev server

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/secrets_engine/config.py

@@ -0,0 +1,43 @@
+"""Runtime configuration resolved from environment and repo layout.
+
+Nothing here is a secret. Backend auth (BAO_TOKEN / bootstrap token files) is
+resolved lazily inside the backend adapter, never cached on disk by this module.
+"""
+from __future__ import annotations
+
+import os
+from dataclasses import dataclass
+from pathlib import Path
+
+
+def repo_root() -> Path:
+    """Repo root = nearest ancestor containing pyproject.toml (fallback: cwd)."""
+    here = Path(__file__).resolve()
+    for parent in (here, *here.parents):
+        if (parent / "pyproject.toml").exists():
+            return parent
+    return Path.cwd()
+
+
+@dataclass(frozen=True)
+class Config:
+    catalog_dir: Path
+    policy_dir: Path
+    evidence_dir: Path
+    hub_url: str
+    bao_addr: str
+    topic_id: str
+
+    @classmethod
+    def load(cls) -> "Config":
+        root = repo_root()
+        return cls(
+            catalog_dir=Path(os.environ.get("SECRETS_ENGINE_CATALOG", root / "catalog")),
+            policy_dir=Path(os.environ.get("SECRETS_ENGINE_POLICIES", root / "policies")),
+            evidence_dir=Path(os.environ.get("SECRETS_ENGINE_EVIDENCE", root / ".evidence")),
+            hub_url=os.environ.get("SECRETS_ENGINE_HUB_URL", "http://127.0.0.1:8000"),
+            bao_addr=os.environ.get("BAO_ADDR", os.environ.get("VAULT_ADDR", "http://127.0.0.1:8200")),
+            topic_id=os.environ.get(
+                "SECRETS_ENGINE_TOPIC_ID", "cee7bedf-2b48-46ef-8601-006474f2ad7a"
+            ),
+        )