feat(panel): tooltip sweep — overview, agents, A2A, journals, auditor, metrics

Derivation tips on every key-metric, scorecard, and quality-metrics
figure; the cryptic member-scorecard headers get full decodes; avatar
initials, truncated ids, and toggle buttons gain accessible names;
title-only hints upgrade to the HelpTip idiom throughout.

panel/src/components/metrics/agent-usage-chart.tsx

@@ -13,6 +13,7 @@ import {
 import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
 import { Skeleton } from "@/components/ui/skeleton";
 import { SegmentedControl } from "@/components/ui/segmented-control";
+import { HelpTip } from "@/components/ui/help-tip";
 import { useIsMobile } from "@/hooks/use-is-mobile";
 import type { AgentUsageRow } from "@/types";
 
@@ -70,7 +71,11 @@ export function AgentUsageChart({ data, isLoading }: AgentUsageChartProps) {
                 <tr>
                   <th className="text-left font-medium py-1">Agent</th>
                   <th className="text-right font-medium py-1">Tokens</th>
-                  <th className="text-right font-medium py-1">%</th>
+                  <th className="text-right font-medium py-1">
+                    <HelpTip label="Share of total tokens across all agents in this window">
+                      <span>%</span>
+                    </HelpTip>
+                  </th>
                 </tr>
               </thead>
               <tbody>