fix: copy button functionality in web browsers

- Add clipboard utility with fallback for non-secure contexts
- Implement modern Clipboard API with document.execCommand fallback
- Update copy buttons in code blocks, markdown, messages, and session list
- Add proper error handling and user feedback for copy operations

Fixes issue where copy buttons did not work in web browsers served over HTTP or without Clipboard API support

packages/ui/src/lib/clipboard.ts

@@ -0,0 +1,61 @@
+/**
+ * Clipboard utility with fallback for non-secure contexts
+ * The modern Clipboard API requires HTTPS or localhost, but document.execCommand
+ * works in HTTP contexts as a fallback.
+ */
+
+import { getLogger } from "./logger"
+
+const log = getLogger("actions")
+
+/**
+ * Copy text to clipboard with fallback for non-secure contexts
+ * @param text - The text to copy
+ * @returns Promise<boolean> - true if successful, false if failed
+ */
+export async function copyToClipboard(text: string): Promise<boolean> {
+  try {
+    // Try modern Clipboard API first (requires secure context)
+    if (typeof navigator !== "undefined" && navigator.clipboard && navigator.clipboard.writeText) {
+      await navigator.clipboard.writeText(text)
+      log.info("Copied text using Clipboard API")
+      return true
+    }
+  } catch (error) {
+    log.warn("Clipboard API failed, trying fallback:", error)
+  }
+
+  // Fallback for non-secure contexts (HTTP) using document.execCommand
+  try {
+    if (typeof document === "undefined") {
+      log.error("Document not available for clipboard fallback")
+      return false
+    }
+
+    // Create temporary textarea element
+    const textArea = document.createElement("textarea")
+    textArea.value = text
+    textArea.style.position = "fixed"
+    textArea.style.left = "-9999px"
+    textArea.style.top = "-9999px"
+    textArea.style.opacity = "0"
+
+    document.body.appendChild(textArea)
+    textArea.focus()
+    textArea.select()
+
+    const success = document.execCommand("copy")
+    document.body.removeChild(textArea)
+
+    if (success) {
+      log.info("Copied text using execCommand fallback")
+      return true
+    } else {
+      log.error("execCommand copy failed")
+      return false
+    }
+  } catch (error) {
+    log.error("Clipboard fallback failed:", error)
+    return false
+  }
+}