fix: handle clipboard write failure in CopyButton, remove duplicate catch

[NubsCarson]

Summary

• CopyButton (packages/ui/src/components/ui/copy-button.tsx): Previously used void navigator.clipboard.writeText(value) which fires-and-forgets the clipboard write, then immediately shows the "copied" checkmark — even when the write fails (permission denied, insecure context, etc.). Now the component awaits the promise and only shows success feedback on actual success.
• CopyButton timer leak: The setTimeout that resets the copied state was never cleaned up on unmount, which could call setCopied on an unmounted component. Added a useRef + cleanup useEffect to clear the timer.
• useDataLoaders (packages/app-core/src/state/useDataLoaders.ts): Removed a duplicate .catch(() => {}) that was chained after an identical .catch(() => {}) — the second handler is unreachable dead code (a caught promise resolves to undefined, so the second catch never fires).

Test plan

• Click the copy button in the chat UI — verify checkmark appears and text is in clipboard
• Revoke clipboard permission (or test in an insecure context like HTTP) — verify the button does NOT show the checkmark
• Rapidly click copy, then navigate away — verify no React warnings about setState on unmounted component
• Verify owner name loading in data loaders still works (no behavioral change from removing the duplicate catch)

🤖 Generated with Claude Code

[github-actions]

Agent Review — Service Unavailable

Both AI reviewers failed to complete the review for this run:

• Claude: failure
• Codex (fallback): failure

This is likely a temporary API outage. The PR will need to be re-reviewed once services recover.

View workflow run

6. Decision: REQUEST CHANGES (automated review unavailable — please re-trigger or wait for service recovery)