[NOTICKET] fix(agents): soften injected reply-language line to a default, not ONLY

The [Reply language] value was injected as 'Respond ONLY in: X', which fought the system prompt's 'default + explicit-request exception' rule and could make the model ignore an explicit 'jawab dalam bahasa Inggris'. Inject just the detected value; the rule (and the override exception) lives in chatbot_system.md.

src/agents/chatbot.py

@@ -127,9 +127,9 @@ def _build_default_chain() -> Runnable:
     prompt = ChatPromptTemplate.from_messages(
         [
             ("system", _load_system_prompt()),
-            # Hard reply-language directive — the system prompt's language rule
-            # points at this. Deterministic + mandatory, mirrors the help path.
-            ("system", "[Reply language]\nRespond ONLY in: {reply_language}"),
+            # Detected default reply language — the system prompt's reply-language
+            # rule reads this value (and defines the explicit-request exception).
+            ("system", "[Reply language] (detected default): {reply_language}"),
             MessagesPlaceholder(variable_name="history", optional=True),
             ("human", "{message}"),
             ("system", "Data context for this turn:\n\n{context}"),