[6.x] Lazy-load actions for assets, collections, submissions & terms

[duncanmcclean]

This pull request avoids sending actions from the server, in favour of lazy-loading them over AJAX when the dropdown is hovered over.

We already do this in the entry listing by just not passing the actions key, so I've copied that over to other places where it makes sense.

[jasonvarga]

Changes via AI review, but confirmed with my browser, eyes, and mouse:

The direction (lazy-load actions for assets, collections, submissions, terms) is good and matches the entry listing. Submissions and terms are safe because they use prepended row actions and the shared Listing with actionUrl/actionContext. Collections are safe with actions_url.

The asset browser is not yet compatible with omitting actions:

1. Guard against undefined actions in AssetBrowserMixin.js (and any other asset browser code that touches folder.actions / asset.actions), e.g. optional chaining: asset.actions?.some(...), folder.actions?.some(...), and equivalent for .find() and .length. Ensure drag/drop and “move” behaviour degrade safely when actions are not yet loaded (or add a path to load them before enabling move).
2. Table view – folder row actions: Either show the folder actions dropdown when actionUrl/context exist (e.g. show when folderActionUrl is set, and pass undefined for :actions so ItemActions lazy-loads on hover), or ensure loadActions is triggered when the user opens the folder actions menu so the dropdown can populate.
3. Grid view: Ensure folder and asset context menus (or dropdowns) either trigger loadActions when opened or handle actions being undefined without throwing (e.g. avoid asset.actions.length when actions may be undefined).

Until the asset browser is updated along these lines, removing actions from FolderAsset (and any asset list payload) will introduce regressions and possible JS errors.

Suggested Changes

• Blocking: In AssetBrowserMixin.js, use optional chaining (or equivalent) wherever asset.actions or folder.actions is used (e.g. canMoveAsset, canMoveFolder, handleFolderDrop), so missing actions does not throw. Decide how move/drag should behave when actions are not loaded (e.g. disable until loaded, or trigger load on first interaction).
• Blocking: In Table.vue, change folder row actions so the dropdown is shown when folder actions can be lazy-loaded (e.g. when folderActionUrl is set), and pass :actions="folder.actions" (so undefined triggers lazy-load in ItemActions). Add a way to trigger loadActions on dropdown/menu open (e.g. @mouseover or equivalent) so actions appear.
• Blocking: In Grid.vue, fix any direct use of asset.actions (e.g. asset.actions.length) so it is safe when actions is undefined; ensure folder/asset menus can trigger loadActions when opened so lazy-loaded actions appear.