Seamless asset refresh instead of the reload prompt

[ernestdefoe]

Background

When the forum's assets are rebuilt — a deploy, or simply an admin enabling/disabling an extension — every API response starts carrying a new X-Flarum-Assets-Revision. ForumApplication.checkAssetsRevision compares it to the revision the page booted with and, if it differs, immediately shows a dismissible "A new version of this page is available — Reload" alert.

Two problems with showing it right away:

• It appears mid-read or mid-compose, interrupting whatever the user was doing.
• Because an extension toggle rebuilds assets, it pops up for every visitor on the forum at once the moment an admin touches the admin area — which reads as the forum nagging everyone to reload.

What this does

Implements the middle ground @luceos proposed — don't interrupt, don't ignore. When newer assets are detected we just remember it (assetsRefreshPending) and say nothing. The user's next real navigation — clicking a link, opening a discussion, back/forward — is turned into a full page load, so the fresh assets are picked up naturally.

The result: an actively reading or typing user is never interrupted, there's no modal and no timing guesswork, no risk of discarding an open draft — and the very next navigation is already on the new assets.

Details

• checkAssetsRevision now sets a flag and lazily wires up refreshOnNextNavigation() instead of showing the alert. It's still public so the realtime extension's pushed revision token flows through the same path.
• refreshOnNextNavigation() adds a capture-phase click listener (stops propagation so it runs before the router's <Link> handling) that only acts on a plain left-click of an internal, same-origin link. It deliberately leaves untouched: modified clicks (Ctrl/⌘/Shift/middle → open in new tab/window), target="_blank" / download links, in-page anchors (#…), javascript: / mailto: / tel: links, external links, and bare hash changes on the current page. popstate reloads too.
• Removed the now-unused Button import.

The core.lib.assets_updated.message / .reload_button locale strings are now unused. I left them in place to avoid churning existing translations — happy to remove them if you'd prefer.

Testing

Verified against a forum whose assets were rebuilt after load:

• No alert appears; the flag is set instead.
• The next internal-link click / back-forward triggers a full page load onto the new assets, while modified clicks, new-tab/download, external, #, javascript: links, and same-page hash changes all behave normally.

I've also been running this as a userland extension (overriding the same method) on two production forums.