[6.x] Inertia user addresses

[riasvdv]

Description

Ports user addresses as a small Inertia wrapper around the legacy NestedElementManager.

Fixes / adapts a few bridges between Inertia and old JS code:

• Separated root CP assets from Inertia page-specific legacy assets in CpScreenResponse.
• Flushed global CP assets before buffering Inertia page assets, so jQuery, Craft, and Craft.NestedElementManager exist before page boot scripts run.
• Captured page-specific headHtml / bodyHtml and passed them as Inertia props.
• Made useAppendHtml() append after Vue’s DOM flush with nextTick + flush: 'post', so v-html content exists before new Craft.NestedElementManager(...) runs.
• Added the legacy .action-btn class back onto generated element action menu triggers, so NestedElementManager.initElement() can find and wire the three-dots menu.
• Fixed CP.js copy callbacks with for (const callback of ...), so the nested manager’s Copy/Paste update path doesn’t throw under strict execution.