Isolate cloud model access before enabling product RAG workflows

The API and ingestion tools now use a fixed internal model gateway while
governed profiles, embedding cache assignments, traceable citations, and
stable API errors establish the boundaries required by later workflows.

Constraint: The current Alibaba Cloud workspace rejects all three live model calls with authentication failures
Rejected: Give the API or seed tools the Bailian key and direct egress | combines database access, cloud credentials, and public network access
Rejected: Mix offline and Bailian vectors in one demo namespace | makes profile activation and retrieval ambiguous
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Keep Bailian credentials and egress exclusive to model-gateway and create a new immutable profile hash for any embedding identity change
Tested: make verify; 121 backend tests; 14 frontend tests; fresh and populated Alembic upgrade-downgrade-upgrade; two idempotent offline seeds; Docker health and HTTP retrieval; isolated provider smoke
Not-tested: Successful live Bailian responses because the supplied workspace credential currently fails authentication

docs/adr/README.md

@@ -8,3 +8,4 @@ ADR 用于记录会长期影响系统的技术决策。状态使用 `proposed`
 - [0002-separate-bailian-protocols.md](0002-separate-bailian-protocols.md)：分离百炼 Chat/Embedding 与 Rerank 协议适配器。
 - [0003-text-first-scope.md](0003-text-first-scope.md)：第一版采用文本优先边界，不宣称地质图空间理解。
 - [0004-secretless-web-ingress.md](0004-secretless-web-ingress.md)：用无 Secret 的 Nginx Web 与固定上游 gateway 隔离浏览器、API 和数据库网络。
+- [0005-isolate-model-egress.md](0005-isolate-model-egress.md)：用独立 Model Gateway 隔离百炼 Key、模型出口与数据库感知服务。