fix(ai): render tool-call arguments as compact JSON in logs

Switch the "Agentic tool call" log from {:?} (Debug) to {} (Display) on
serde_json::Value. Display produces compact JSON — `{"date":"2023-08-15"}`
instead of `Object {"date": String("2023-08-15")}` — which is what the
model actually sent and what a human reading the log wants to see.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ai/insight_generator.rs

@@ -3281,7 +3281,7 @@ Return ONLY the summary, nothing else."#,
             {
                 for tool_call in tool_calls {
                     log::info!(
-                        "Agentic tool call [{}]: {} {:?}",
+                        "Agentic tool call [{}]: {} {}",
                         iteration,
                         tool_call.function.name,
                         tool_call.function.arguments