style(usage): show reasoning effort under the model name

Drop the separate reasoning-effort column from request details and render the raw effort, or auto, directly beneath the model name. Include it in the model tooltip, reset saved layouts that still use the old default column, and keep the field in CSV export.

src/pages/UsageEventsView.css

@@ -162,6 +162,19 @@
   margin-top: 2px;
 }
 
+.usage-request-log .usage-events-table .usage-td-model > .usage-model-effort {
+  display: block;
+  width: fit-content;
+  max-width: 100%;
+  margin-top: 2px;
+  overflow: hidden;
+  color: var(--usage-log-muted);
+  font-size: 10px;
+  line-height: 1.4;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
 .usage-request-log .usage-events-table .usage-td-model > .usage-response-model {
   color: var(--usage-log-response-model);
 }