fix: remove redundant try_it_out tool rule from system prompt

Explicit 'Use try_it_out when...' instruction duplicates what the tool
description already declares. Tool descriptions are the right place
for capability/trigger declarations; the system prompt is for:
- multi-step confirm flows (create_plugin/publish_plugin gates)
- post-call state transitions
- fallback behaviors on tool failure
- cross-cutting policy exceptions (anti-hallucination EXCEPTION clause)

The real fixes (anti-hallucination exception + unambiguous template_id
message format) remain in place.

src/api/routers/chat.py

@@ -531,11 +531,6 @@ def _build_system_prompt(
         "exist yet, reply: 'To save memories you need a memory agent first. "
         "I can create one for you — just say **create a memory agent**.'"
         " Then include [button:Create Memory Agent:/agents?spawn=1&skill=memory+agent].\n"
-        "- Use `try_it_out` when message contains 'try-it-out', 'tryit', '/tryit', 'run demo', "
-        "'show me demo', or 'template_id='. Pass the template_id exactly as given. "
-        "IMPORTANT: try_it_out creates its own demo agent automatically — it does NOT require "
-        "any pre-existing agent or plugin in DATA REGISTRY. Never refuse a try_it_out request "
-        "because of missing agents.\n"
         "- Answer in markdown for all other questions.\n\n"
         "Response formatting rules:\n"
         "- ALWAYS embed inline links when you mention any NebulaOS page or feature. "