Fix Alpine bug with missing "theme" property, and lazy-load CSS/JS assets

[jackwh]

This PR fixes two issues raised in #3.

1. theme is undefined

• When enforcing dark mode in Filament with $panel->darkMode(true, true), theme was undefined. This caused Alpine to throw console errors.
• I fixed this by initialising the theme property from Filament's localStorage key, falling back to the panel's default theme mode.

2. SyntaxEntry components in a modal seemed to have no effect

• When opening a modal with a SyntaxEntry I noticed the hljs.highlightElement(el) method wasn't being called, so the new elements were remaining unaffected.
• The component uses x-load-js and x-load-css, which I assume (?) was added with the intention of lazy-loading the assets.
• However, the service provider registered its Filament assets without specifying loadedOnRequest().
• This meant the assets were being bundled on every page (undesirable), and the lazy-loading had no effect.
• By loading on request, the component now works again when launched inside a modal.

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Quick addendum re custom themes:

This package seems tightly coupled to the Filament base theme. Some styles were being overloaded when used with the Filament Minimal Theme. I was able to work around this by publishing the vendor views and commenting out x-load-css, but ideally this could be fixed in a future update.