fix(context): show both summarize and compress thresholds in /context

The /context command previously showed only the hard budget compression
threshold (contextWindow - maxTokens), which confused users who expected
to see the soft summarization trigger from summarize_token_percent.

This commit adds SummarizeAtTokens alongside the existing CompressAtTokens
so that both thresholds are visible:

- Compress at: contextWindow - maxTokens (hard budget, triggers proactive
  compression when exceeded)
- Summarize at: contextWindow * summarizeTokenPercent / 100 (soft trigger,
  matches maybeSummarize's threshold)

The fix updates the /context command output, the Web UI popover, and the
pico channel WebSocket payload.

Fixes #2968

web/frontend/src/components/chat/context-usage-ring.tsx

@@ -145,6 +145,23 @@ export function ContextUsageRing({
             />
           </div>
 
+          <div className="mt-2 space-y-0.5">
+            <div className="flex items-center justify-between text-[10px]">
+              <span className="text-muted-foreground">Compress at</span>
+              <span className="tabular-nums">
+                {formatTokens(usage.compress_at_tokens)}
+              </span>
+            </div>
+            {usage.summarize_at_tokens != null && usage.summarize_at_tokens > 0 && (
+              <div className="flex items-center justify-between text-[10px]">
+                <span className="text-muted-foreground">Summarize at</span>
+                <span className="tabular-nums">
+                  {formatTokens(usage.summarize_at_tokens)}
+                </span>
+              </div>
+            )}
+          </div>
+
           <button
             type="button"
             onClick={handleDetail}