feat: add copy button to code blocks in agent output (#1598)

## Problem

When the agent outputs code blocks (e.g. SQL queries, shell commands), there is no way to copy the code without manually selecting it.

Fixes #1499

## Solution

Added a hover-to-reveal copy button to the `CodeBlock` component used by `MarkdownRenderer`. The button:

- Appears in the top-right corner on hover (`group-hover`)
- Uses the same `Copy`/`Check` icon pattern from `@phosphor-icons/react` already used in `AgentMessage.tsx`
- Copies code text to clipboard via `navigator.clipboard.writeText`
- Shows a ✓ checkmark for 2 seconds after copying
- Uses `IconButton` from `@radix-ui/themes` for consistent styling

## Files Changed

- `apps/code/src/renderer/components/CodeBlock.tsx` — wrapped in relative div with `group` class, added `IconButton` with copy logic

Author: reverb256

apps/code/src/renderer/components/CodeBlock.tsx

@@ -1,4 +1,7 @@
+import { Check, Copy } from "@phosphor-icons/react";
+import { IconButton } from "@radix-ui/themes";
 import type { ReactNode } from "react";
+import { useCallback, useState } from "react";
 
 type CodeBlockSize = "1" | "1.5" | "2" | "3";
 
@@ -29,27 +32,67 @@ const sizeStyles: Record<
   },
 };
 
+function extractText(children: ReactNode): string {
+  if (typeof children === "string") return children;
+  if (Array.isArray(children)) return children.map(extractText).join("");
+  if (children && typeof children === "object" && "props" in children) {
+    return extractText(
+      (children as { props: { children?: ReactNode } }).props.children,
+    );
+  }
+  return "";
+}
+
 export function CodeBlock({ children, size = "1" }: CodeBlockProps) {
   const styles = sizeStyles[size];
+  const [copied, setCopied] = useState(false);
+
+  const handleCopy = useCallback(() => {
+    const text = extractText(children);
+    navigator.clipboard.writeText(text);
+    setCopied(true);
+    setTimeout(() => setCopied(false), 2000);
+  }, [children]);
 
   return (
-    <pre
-      style={{
-        margin: 0,
-        marginBottom: "var(--space-3)",
-        padding: "var(--space-3)",
-        backgroundColor: "var(--gray-2)",
-        borderRadius: "var(--radius-2)",
-        border: "1px solid var(--gray-4)",
-        fontFamily: "var(--code-font-family)",
-        fontSize: styles.fontSize,
-        lineHeight: styles.lineHeight,
-        color: "var(--gray-12)",
-        overflowX: "auto",
-        whiteSpace: "pre",
-      }}
-    >
-      {children}
-    </pre>
+    <div className="group" style={{ position: "relative" }}>
+      <pre
+        style={{
+          margin: 0,
+          marginBottom: "var(--space-3)",
+          padding: "var(--space-3)",
+          paddingRight: "var(--space-7)",
+          backgroundColor: "var(--gray-2)",
+          borderRadius: "var(--radius-2)",
+          border: "1px solid var(--gray-4)",
+          fontFamily: "var(--code-font-family)",
+          fontSize: styles.fontSize,
+          lineHeight: styles.lineHeight,
+          color: "var(--gray-12)",
+          overflowX: "auto",
+          whiteSpace: "pre",
+        }}
+      >
+        {children}
+      </pre>
+      <IconButton
+        size="1"
+        variant="ghost"
+        color="gray"
+        onClick={handleCopy}
+        style={{
+          position: "absolute",
+          top: "var(--space-1)",
+          right: "var(--space-1)",
+          opacity: 0,
+          transition: "opacity 0.15s",
+          cursor: "pointer",
+        }}
+        className="group-hover:!opacity-100 [&]:hover:!opacity-100"
+        aria-label="Copy code"
+      >
+        {copied ? <Check size={14} /> : <Copy size={14} />}
+      </IconButton>
+    </div>
   );
 }