fix: copy button fallback for non-secure contexts (#2472)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - The UI serves agent management pages including an instructions editor with copy-to-clipboard buttons
> - The Clipboard API (`navigator.clipboard.writeText`) requires a secure context (HTTPS or localhost)
> - Users accessing the UI over HTTP on a LAN IP get "Copy failed" when clicking the copy icon
> - This pull request adds an `execCommand("copy")` fallback in `CopyText` for non-secure contexts
> - The benefit is that copy buttons work reliably regardless of whether the page is served over HTTPS or plain HTTP

## What Changed

- `ui/src/components/CopyText.tsx`: Added `window.isSecureContext` check before using `navigator.clipboard`. When unavailable, falls back to creating a temporary `<textarea>`, selecting its content, and using `document.execCommand("copy")`. The return value is checked and the DOM element is cleaned up via `try/finally`.

## Verification

- Access the UI over HTTP on a non-localhost IP (e.g. `http://[local-ip]:3100`)
- Navigate to any agent's instructions page → Advanced → click the copy icon next to Root path
- Should show "Copied!" tooltip and the path should be on the clipboard

## Risks

- Low risk. `execCommand("copy")` is deprecated in the spec but universally supported by all major browsers. The fallback only activates in non-secure contexts where the modern API is unavailable. If/when HTTPS is enabled, the modern `navigator.clipboard` path is used automatically.

## Checklist

- [x] I have included a thinking path that traces from project context to this change
- [ ] I have run tests locally and they pass
- [ ] I have added or updated tests where applicable
- [ ] If this change affects the UI, I have included before/after screenshots
- [ ] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before requesting merge

ui/src/components/CopyText.tsx

@@ -18,7 +18,23 @@ export function CopyText({ text, children, className, copiedLabel = "Copied!" }:
 
   const handleClick = useCallback(async () => {
     try {
-      await navigator.clipboard.writeText(text);
+      if (navigator.clipboard && window.isSecureContext) {
+        await navigator.clipboard.writeText(text);
+      } else {
+        // Fallback for non-secure contexts (e.g. HTTP on non-localhost)
+        const textarea = document.createElement("textarea");
+        textarea.value = text;
+        textarea.style.position = "fixed";
+        textarea.style.left = "-9999px";
+        document.body.appendChild(textarea);
+        try {
+          textarea.select();
+          const success = document.execCommand("copy");
+          if (!success) throw new Error("execCommand copy failed");
+        } finally {
+          document.body.removeChild(textarea);
+        }
+      }
       setLabel(copiedLabel);
     } catch {
       setLabel("Copy failed");