feat(developer): add hybrid iframe integration for developer tools

Replace placeholder pages with ToolEmbed component that embeds
LangGraph, LangFlow, and Langfuse in iframes when configured, or
shows "Not Configured" placeholders when URLs are empty. Add
ServiceUrlsContext for passing service URLs through Dioxus context.

Add docker-compose services for local development: LangFlow,
LangGraph (trial), Langfuse with full dependency stack (Postgres,
ClickHouse, Redis, MinIO).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.env.example

@@ -66,10 +66,11 @@ STRIPE_WEBHOOK_SECRET=
 STRIPE_PUBLISHABLE_KEY=
 
 # ---------------------------------------------------------------------------
-# LangChain / LangGraph / Langfuse [OPTIONAL]
+# LangChain / LangGraph / LangFlow / Langfuse [OPTIONAL]
 # ---------------------------------------------------------------------------
 LANGCHAIN_URL=
 LANGGRAPH_URL=
+LANGFLOW_URL=
 LANGFUSE_URL=
 
 # ---------------------------------------------------------------------------