feat: add soul.md for system prompt configuration and update .gitignore

.gitignore

@@ -14,3 +14,4 @@
 .idea/
 Thumbs.db
 .DS_Store
+SOUL.md

config.toml.global.template

@@ -29,8 +29,5 @@ ai_retries = 2
 # Valid range 1-65535; leave unset to disable the panel.
 # web_port = 8080
 
-# System prompt defining the responder's identity (required for the AI autoreply).
-system_prompt = """
-# Identity
-You are human........
-"""
+# The system prompt (required for the AI autoreply) is not set here:
+# write it in soul.md, next to this file (see soul.md.template).

soul.md.template

@@ -0,0 +1,2 @@
+# Identity
+You are human........