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>

src/infrastructure/config.rs

@@ -154,6 +154,8 @@ pub struct ServiceUrls {
     pub langchain_url: String,
     /// LangGraph service URL.
     pub langgraph_url: String,
+    /// LangFlow visual workflow builder URL.
+    pub langflow_url: String,
     /// Langfuse observability URL.
     pub langfuse_url: String,
     /// Vector database URL.
@@ -183,6 +185,7 @@ impl ServiceUrls {
                 .unwrap_or_else(|_| "http://localhost:8888".into()),
             langchain_url: optional_env("LANGCHAIN_URL"),
             langgraph_url: optional_env("LANGGRAPH_URL"),
+            langflow_url: optional_env("LANGFLOW_URL"),
             langfuse_url: optional_env("LANGFUSE_URL"),
             vectordb_url: optional_env("VECTORDB_URL"),
             s3_url: optional_env("S3_URL"),