Add /clear command

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

web/src/components/ChatView.tsx

@@ -459,13 +459,15 @@ const MessageItem = memo(function MessageItem({ m, canEdit, onRewind, highlight
     return (
       <details className="summary-divider" data-mid={m.id} onToggle={(e) => setSummaryOpen((e.currentTarget as HTMLDetailsElement).open)}>
         <summary>
-          {summary.auto
+          {summary.text.startsWith("[Context cleared")
+            ? t("chat.cleared")
+            : summary.auto
             ? t("chat.compactedAuto", { tokens: summary.tokens ? fmtCompact(summary.tokens) : "?" })
             : summary.tokens
               ? t("chat.compactedManual", { tokens: fmtCompact(summary.tokens) })
               : t("chat.compacted")}
         </summary>
-        {summaryOpen && <Markdown text={summary.text} />}
+        {summaryOpen && !summary.text.startsWith("[Context cleared") && <Markdown text={summary.text} />}
       </details>
     );
   }

web/src/components/Composer.tsx

@@ -20,6 +20,7 @@ interface Suggestion {
 
 const BUILTIN: { name: string; key: Key }[] = [
   { name: "compact", key: "command.compact" },
+  { name: "clear", key: "command.clear" },
   { name: "new", key: "command.new" },
 ];