Update transaction_type normalization in extract_and_update_intent function

- Changed the normalization guideline for the transaction_type field from 'buy' to 'sale' to better reflect terminology consistency.
- This update enhances the clarity of intent handling related to transaction types, ensuring more accurate user interactions.

ai_chat.py

@@ -256,7 +256,7 @@ async def extract_and_update_intent(state):
        - If adding: Include both existing and new items in the array
        - If changing: Replace with new requirements
        - If clarifying: Update with more specific versions
-    3. For transaction_type field: Normalize to either 'lease' or 'buy':
+    3. For transaction_type field: Normalize to either 'lease' or 'sale':
        - 'rent', 'rental', 'lease', 'leasing', 'to rent' → 'rent'
        - 'buy', 'purchase', 'buying', 'sale', 'for sale', 'to buy' → 'buy'
     4. If the user is asking a definition or clarification (e.g. 'What does square metre mean?'), answer that question fully and do not update the intent.