ux: add tooltip to copy button in Launcher notification

[weiningwei]

What

Shows a transient checkmark icon as visual feedback when the user copies a notification message, then resets back to the copy icon after one second.

Changes

• Make Notification observable (ObservableObject) and add an IsCopied property.
• Toggle between the copy icon and a green checkmark in the launcher notification item based on IsCopied.
• Add a DispatcherTimer in LauncherPage to reset IsCopied one second after copying.
• Add a tooltip to the copy button.

[JC-Chung]

Hi @weiningwei, thanks for this PR! I ran into the same need for CommitBaseInfo's SHA copy button and, as a follow-up, ended up building a reusable CopyButton control (#2668), covering both LauncherPage and CommitBaseInfo. It touches the same lines in LauncherPage.axaml(.cs), so merging both would conflict. Would you be open to rebasing this on top of CopyButton so we land on one consistent solution? Happy to help adjust either side.

[weiningwei]

Hi @JC-Chung, congrats on #2668 being merged — the reusable CopyButton is a nice cleanup, and thanks for the heads-up here.
I've rebased this PR on top of it. Since the notification copy feedback is now fully covered by CopyButton, this PR is reduced to a single line: adding the missing Text.Copy tooltip to the CopyButton in LauncherPage — the same tooltip CommitBaseInfo already has, so both usages stay consistent.
@love-linger Just want to confirm: is this one-liner worth keeping as a separate PR, or would you rather not have the tooltip there at all? Happy to close if it's unnecessary.

[JC-Chung]

I did notice the tooltip aspect, but since the dismiss button next to it doesn't have one either, I kept it as-is. If we're adding one now, maybe we should also consider adding a tooltip to the dismiss button? No rush to change it right away though — might be worth waiting to hear what the @love-linger think first.