docs(policy): enforce server-side data ownership and backend LLM mediation

- clarify frontend may only rely on backend-issued session token cookie for auth

- forbid frontend browser storage for domain/business data

- require backend-mediated LLM calls across agent workflows

.github/agents/frontend.agent.md

@@ -39,6 +39,8 @@ frontend/src/
 7. **Routes:** new pages go in `src/pages/`, registered in `src/router/index.tsx`, lazy-loaded.
 8. **Strings:** no hardcoded user-facing strings outside of constants.
 9. **No over-engineering:** only add what is explicitly needed — no extra abstractions, helpers, or features.
+10. **Data ownership:** domain/business data must stay server-side; frontend never persists entities, tasks, generated messages, logs, or similar domain data in `localStorage`, `sessionStorage`, or `IndexedDB`.
+11. **LLM calls:** frontend must never call OpenAI/Ollama/Llama directly; use backend APIs only.
 
 ## TDD Cycle
 
@@ -59,4 +61,5 @@ frontend/src/
 - DO NOT store server data in `useState`.
 - DO NOT build custom UI primitives when a shadcn/ui component exists.
 - DO NOT write implementation code before the failing test exists.
-- DO NOT modify backend code — your scope is `frontend/` only.
+- DO NOT modify backend code — your scope is `frontend/` only.
+- DO NOT store business/domain data in browser storage; only the backend-issued `httpOnly` session cookie is allowed for auth state.