Fix engram_compile: fetch pinned nodes directly when vector search empty

Replace scan-by-offset fallback with engram_get_node_json calls for the
known high-salience identity nodes (family, origin). Offset-based scanning
is order-dependent and unreliable; direct ID fetch is stable regardless of
snapshot position. Ensures biographical context (Fox, Bobby, etc.) is
always in the system prompt when vector search returns nothing.

chat.elh

@@ -5,6 +5,7 @@ extern fn json_safe(s: String) -> String
 extern fn build_system_prompt(ctx: String) -> String
 extern fn hist_append(hist: String, role: String, content: String) -> String
 extern fn hist_trim(hist: String) -> String
+extern fn clean_llm_response(s: String) -> String
 extern fn handle_chat(body: String) -> String
 extern fn handle_see(body: String) -> String
 extern fn studio_tools_json() -> String