feat(webui): read-only workflow policy & guardrail visibility (Closes #646)

Phase 3 child of the Web Console epic #631. Operators can now see the active
workflow policy/guardrail configuration from the console instead of reading the
repo tree.

- webui/policy_inventory.py (new): redacted, machine-readable guardrail
  inventory. One row per major guardrail (role separation/RBAC, lease rules,
  worktree binding, merge confirmation, redaction, contamination, allocator
  policy, audit logging, mutation gating) with source pointers (file/module/doc)
  and a compact active projection from the existing safe policy accessors.
  Fail-soft per entry; whole payload run through console_redaction before emit;
  diff vs documented default where feasible.
- webui/policy_views.py (new): HTML cards with source pointers, active config,
  and the documented-default diff; read-only page copy, no forms.
- webui/app.py: register GET /policy and GET /api/v1/policy (additive).
- webui/layout.py: add Policy nav item.
- tests/test_webui_policy_visibility.py (new): guardrail presence + source
  pointers (AC1), redaction incl. planted-secret masking and scan_for_secrets
  (AC2/AC3), read-only page + no-mutation routes (AC4), fail-soft rendering.
- docs/webui-local-dev.md: route table + read-only policy-visibility section.

Read-only throughout; no policy editing, no gate-weakening toggle, secrets
redacted.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

docs/webui-local-dev.md

@@ -64,6 +64,8 @@ status, onboarding checklist state, and the fail-closed error payloads (#635).
 | `/api/prompts` | JSON prompt export with workflow hashes |
 | `/runtime` | MCP runtime health and stale detection (#430) |
 | `/api/runtime` | JSON runtime health export |
+| `/policy` | Workflow policy and guardrail configuration visibility (#646) |
+| `/api/v1/policy` | Versioned JSON guardrail inventory (redacted, read-only) |
 | `/audit` | Report audit paste + validator preview (#431) |
 | `/api/audit` | JSON validator preview (POST `report_text`, optional `task_kind`) |
 | `/worktrees` | Worktree hygiene dashboard (#432) |
@@ -153,6 +155,19 @@ health, workflow/schema SHA-256 hashes, and stale-runtime warnings when the
 checkout is behind merged safety-gate changes. Restart guidance links to #420;
 no tokens or MCP restart actions are exposed.
 
+## Policy & guardrail visibility (#646)
+
+`/policy` (HTML) and `/api/v1/policy` (JSON) surface a **read-only** projection
+of the major workflow guardrails — role separation/RBAC, lease lifecycle,
+author worktree binding, merge confirmation, secret redaction, contamination
+containment, allocator policy, audit logging, and mutation gating. Each entry
+carries source pointers to the file/module/doc that owns it, a compact active
+value derived from the existing safe policy accessors, and — where a documented
+default is declared — a diff of active vs documented. The whole payload is run
+through the console redaction pass before it is emitted, so a planted or
+accidental secret degrades to the placeholder rather than reaching a client.
+The view never edits policy and exposes no gate-weakening toggle.
+
 ## Deployment boundary (#435)
 
 MVP serves on loopback by default. Binding `0.0.0.0` or `::` is **refused**