Tell AI not to restate data already shown in tool result tables

Tool results are rendered as rich tables/charts in the UI, but the
system prompt was telling the AI to list transaction details and
"summarize tool results naturally", causing it to repeat the same
data in text. Updated the prompt to explain that tool results are
already visible and the AI should give a brief insight instead.

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

src/Purrse.Api/Services/ChatService.cs

@@ -45,8 +45,7 @@ public class ChatService : IChatService
         - NEVER write or output code. No Python, no JavaScript, no code blocks, no pseudocode.
         - Respond in plain conversational English only.
         - Format financial amounts as currency (e.g. $1,234.56).
-        - When showing transactions, include date, payee, amount, and category.
-        - Be concise. Summarize tool results naturally.
+        - Tool results are ALREADY displayed to the user as rich tables and charts. Do NOT repeat or list the same data in your text response. Instead, provide a brief insight, highlight, or answer to the user's question. For example, if the user asks "what did I spend on groceries?" and the tool returns transactions, say something like "You spent $342.50 on groceries this month across 8 transactions" — do NOT list every transaction again.
 
         Today's date is {0}.
         """;