feat(22-03): add ChatStopButton and ChatMessageActions components

- ChatStopButton: centered outline button with Square icon and 'Stop generating' label
- ChatMessageActions: edit Pencil for user messages (absolute, group-hover)
- ChatMessageActions: retry RefreshCw for assistant messages (right-aligned, group-hover)
- Both action buttons return null when isStreaming is true
- Proper aria-labels and tooltips on all interactive elements

ui/src/components/ChatMessageActions.tsx

@@ -0,0 +1,58 @@
+import { Pencil, RefreshCw } from "lucide-react";
+import { Button } from "@/components/ui/button";
+import { Tooltip, TooltipContent, TooltipTrigger } from "@/components/ui/tooltip";
+
+interface ChatMessageActionsProps {
+  role: "user" | "assistant" | "system";
+  isStreaming?: boolean;
+  onEdit?: () => void;
+  onRetry?: () => void;
+}
+
+export function ChatMessageActions({ role, isStreaming, onEdit, onRetry }: ChatMessageActionsProps) {
+  if (isStreaming) return null;
+
+  if (role === "user" && onEdit) {
+    return (
+      <div className="absolute top-1 right-1 hidden group-hover:flex">
+        <Tooltip>
+          <TooltipTrigger asChild>
+            <Button
+              variant="ghost"
+              size="icon"
+              className="h-6 w-6"
+              onClick={onEdit}
+              aria-label="Edit message"
+            >
+              <Pencil className="h-3.5 w-3.5" />
+            </Button>
+          </TooltipTrigger>
+          <TooltipContent>Edit message</TooltipContent>
+        </Tooltip>
+      </div>
+    );
+  }
+
+  if (role === "assistant" && onRetry) {
+    return (
+      <div className="flex justify-end mt-1">
+        <Tooltip>
+          <TooltipTrigger asChild>
+            <Button
+              variant="ghost"
+              size="icon"
+              className="h-6 w-6 hidden group-hover:inline-flex"
+              onClick={onRetry}
+              aria-label="Retry response"
+            >
+              <RefreshCw className="h-3.5 w-3.5" />
+            </Button>
+          </TooltipTrigger>
+          <TooltipContent>Retry response</TooltipContent>
+        </Tooltip>
+      </div>
+    );
+  }
+
+  return null;
+}

ui/src/components/ChatStopButton.tsx

@@ -0,0 +1,23 @@
+import { Square } from "lucide-react";
+import { Button } from "@/components/ui/button";
+
+interface ChatStopButtonProps {
+  onStop: () => void;
+}
+
+export function ChatStopButton({ onStop }: ChatStopButtonProps) {
+  return (
+    <div className="flex justify-center py-2 border-t border-border">
+      <Button
+        variant="outline"
+        size="sm"
+        onClick={onStop}
+        aria-label="Stop generating response"
+        className="gap-1.5"
+      >
+        <Square className="h-3 w-3 fill-current" />
+        Stop generating
+      </Button>
+    </div>
+  );
+}