fix: authorize flow management, gate runs, token-gate callbacks, strict tenants

CHANGELOG.md

@@ -5,6 +5,15 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Security
+- API authorization: flow management is admin-only, runs and run/approval
+  reads require login with strict session-tenant scoping, approval
+  decisions record the session user, and flow callbacks authenticate with
+  a shared `X-Callback-Token` (`CALLBACK_TOKEN`). Request-controlled
+  `tenant_id`, `callback_base_url` and `continuation_flow_id` were
+  removed (SSRF / cross-tenant / flow-chaining hardening);
+  continuations now resolve from the admin-authored definition.
+- Frontend: `/app/*` routes require login; approver is the session user.
 ### Added
 - Landing page: status-quo problem block, 5-step process with quote,
   portal overview with admin areas, AI platform parts, exception tiers,