fix: fall back when sidebar clipboard writes fail

[lawrence3699]

Fixes #913.

Summary

• add a Sidebar clipboard helper that falls back to document.execCommand("copy") when navigator.clipboard.writeText is rejected or unavailable
• keep the existing success UX for both copy buttons and preserve the destructive error toast when every copy path fails
• add regression coverage for both the fallback-success path and the full-failure path

Testing

• npm test -- --runTestsByPath src/components/tests/Sidebar.test.tsx
• npm run lint
• npm run build
• npx prettier --check client/src/components/Sidebar.tsx client/src/components/tests/Sidebar.test.tsx

[Copilot]

Pull request overview

Adds a resilient clipboard-copy implementation in the Sidebar to fix copy failures (Issue #913) by falling back to document.execCommand("copy"), while preserving existing success/error toasts and adding regression tests.

Changes:

• Introduce a copyTextToClipboard helper with an execCommand("copy") fallback when navigator.clipboard.writeText is unavailable or rejected.
• Update both Sidebar copy handlers to use the helper while keeping existing UX/toast behavior.
• Add Sidebar tests covering fallback-success and full-failure scenarios.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
client/src/components/Sidebar.tsx	Adds clipboard helper + routes copy actions through it with fallback logic.
client/src/components/tests/Sidebar.test.tsx	Adds regression tests for fallback success and full failure of clipboard copying.

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[Copilot]

fallbackCopy calls document.execCommand("copy") without checking that execCommand exists/is callable. In browsers/environments where execCommand is missing, this will throw a TypeError and surface a confusing error message (and bypass the intended "Clipboard copy failed" UX). Consider guarding with typeof document.execCommand === "function" and throwing a consistent Error("Clipboard copy failed") (or similar) when unavailable.

Suggested change

	copied = document.execCommand("copy");
	if (typeof document.execCommand !== "function") {
	throw new Error("Clipboard copy failed");
	}
	try {
	copied = document.execCommand("copy");
	} catch {
	throw new Error("Clipboard copy failed");
	}

[Copilot]

The new branch that handles navigator.clipboard.writeText being unavailable (if (!navigator.clipboard?.writeText)) isn't covered by a regression test. Adding a test case where navigator.clipboard (or writeText) is missing would help ensure the fallback path works in insecure contexts/older browsers.