[AI-101] Add the AI actions dropdown to the full editor toolbar

[tangopium]

Ticket

https://community.openproject.org/wp/AI-101

Paired core PR: opf/openproject#25770 (carries the rebuilt bundle; merge both together, never one alone).

What are you trying to accomplish?

Adds an "Assistant" split button at the right end of the full editor toolbar, the entry point for the AI text transform actions of the work package description editor. Ported to the TypeScript and esbuild layout after #135 to #139.

• src/plugins/op-ai-actions/op-ai-actions.ts: split button built from createDropdown with SplitButtonView and addListToDropdown. It asks the core's aiActions service (reached through the plugin context) for the actions of the current resource and field, adds nothing while the list is empty, and hands the selected action back to the service's run. The main part shows the sparkle icon and the name of the action to run: the one the core's optional defaultAction picks (the action run last, else the first), following every selection from the list. Clicking it runs that action; the arrow opens the list. The button carries an "Assistant" tooltip and is disabled while the editor is read-only or in source mode.
• The dropdown is appended to the toolbar element itself, outside the item collections, and keeps itself behind the overflow menu, so it stays visible at every editor width; a maxWidth nudge makes CKEditor regroup its items when the dropdown appears and after every label change.
• src/icons/sparkle.svg is the single sparkle Octicon of the Artificial Intelligence administration section, placed in a 20 unit viewBox like CKEditor's own icons so it renders at their size; registration in op-plugins.ts, aiActions typed in op-types.ts.
• tests/plugins/op-ai-actions.test.ts covers the absent state, the pinned placement and regrouping, the shown action and its fallbacks, the main button and the list, keyboard reachability, the read-only and source mode states and the lifecycle; tests/stubs/svg.ts and a jest.config.js mapping make the icon import testable.

What approach did you choose and why?

The plugin is kept thin on purpose: it renders labels and reports a selection, nothing more. Which actions exist, whether the assistant is available, and what happens on selection all live in the core, so iterating on the editor behaviour does not need a bundle rebuild. On cores that provide no aiActions service the plugin registers nothing, so older OpenProject versions bundling this build see no change.

The caption js.editor.ai_actions.caption comes from the core's locale, like the other toolbar captions.

[myabc]

unfortunately this will now needs some changes (i,e, migration to TS). apologies for the breakage due to #135, #136, #137. Ping me if you need a hand!

[tangopium]

Ported to the TypeScript and esbuild layout and rebased on master in 5c1b3dd. The dropdown now sits on the toolbar element outside the grouped items (it has to stay visible at every width) and uses the sparkle Octicon of the AI administration section; the paired core PR opf/openproject#25770 carries the bundle rebuilt from this branch.