Add user_template to wrap user messages with sender context (name, id, username)

Configure via ai.prompt.user_template in config.json using {text}, {full_name},
{user_id}, {first_name}, {last_name}, {username} placeholders. Applied to both
history user messages and the current prompt. No-op when unset.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/ai/service.py

@@ -289,6 +289,27 @@ class AIService:
             ]
         ).strip()
 
+    def _render_user_message(self, text: str, user: Any) -> str:
+        template = self.config.prompt.user_template
+        if not template or not text:
+            return text
+        first_name = str(getattr(user, "first_name", "") or "")
+        last_name = str(getattr(user, "last_name", "") or "")
+        username = str(getattr(user, "username", "") or "")
+        user_id = str(getattr(user, "id", "") or "")
+        full_name = f"{first_name} {last_name}".strip() or username or user_id
+        try:
+            return template.format_map({
+                "text": text,
+                "user_id": user_id,
+                "first_name": first_name,
+                "last_name": last_name,
+                "username": username,
+                "full_name": full_name,
+            })
+        except (KeyError, ValueError):
+            return text
+
     async def build_messages(
         self,
         ctx: "CommandContext",
@@ -303,8 +324,13 @@ class AIService:
         for item in history:
             if not item.text:
                 continue
-            messages.append({"role": item.role, "content": item.text})
-        messages.append({"role": "user", "content": prompt})
+            if item.role == "user":
+                sender = getattr(item.message, "from_user", None)
+                content = self._render_user_message(item.text, sender)
+            else:
+                content = item.text
+            messages.append({"role": item.role, "content": content})
+        messages.append({"role": "user", "content": self._render_user_message(prompt, ctx.actor)})
         return messages
 
     async def _fetch_mcp_tool_schemas(self) -> list[dict]: