feat: capture function calls from Google + block follow-up quota waste

When MITM strips LS tools and injects custom tools:
- Google returns functionCall → captured in MitmStore
- Follow-up LS requests are blocked with fake SSE response
- Proxy consumes captured calls and clears the flag
- Result: 1 real Google API call instead of 5+ per tool call

Flow: Client → Proxy → LS → MITM(inject tool) → Google
      Google returns functionCall → MITM captures it
      LS tries follow-up → MITM blocks (fake response)
      Proxy reads captured functionCall → returns to client

src/api/responses.rs

@@ -361,6 +361,16 @@ async fn handle_responses_sync(
         uuid::Uuid::new_v4().to_string().replace('-', "")
     );
 
+    // Check for captured function calls from MITM (clears the active flag)
+    let captured_tool_calls = state.mitm_store.take_any_function_calls().await;
+    if let Some(ref calls) = captured_tool_calls {
+        info!(
+            count = calls.len(),
+            tools = ?calls.iter().map(|c| &c.name).collect::<Vec<_>>(),
+            "Consumed captured function calls from MITM"
+        );
+    }
+
     let (usage, mitm_thinking) = usage_from_poll(&state.mitm_store, &cascade_id, &poll_result.usage, &params.user_text, &poll_result.text).await;
 
     // Thinking text priority: MITM-captured (raw API) > LS-extracted (steps)