fix: helion string literal + memory brief anti-echo in Router

- Fixed unquoted `helion` variable reference to string literal `"helion"`
  in tool_manager.py search_memories fallback
- Replaced `[Контекст пам'яті]` with `[INTERNAL MEMORY - do NOT repeat
  to user]` in all 3 injection points in main.py
- Verified: Senpai now responds without Helion contamination or memory
  brief leaking

Tested and deployed on NODE1.

Co-authored-by: Cursor <cursoragent@cursor.com>

services/router/tool_manager.py

@@ -393,7 +393,7 @@ class ToolManager:
             if memory_retrieval and memory_retrieval.qdrant_client:
                 results = await memory_retrieval.search_memories(
                     query=query,
-                    agent_id=agent_id or helion,
+                    agent_id=agent_id or "helion",
                     limit=5
                 )