refactor: create RTE with presets

[kevinkim-ogp]

TL;DR

• Removes the "What would you like to do?" dropdown
• Creates a new RTE component that shows the "presets" on the right of the RTE

What changed?

• Removed the promptType dropdown field from the Pair send-prompt action. Preset selection is now handled directly within the rich-text editor UI.
• Introduced a PROMPT_PRESETS constant that defines the available presets (Summarise, Analyse, Categorise, Write) with labels and descriptions.
• Refactored DEFAULT_PROMPT_VALUES HTML templates from dedent template literals to arrays of HTML fragments joined with '', preventing the editor from introducing unintended extra line breaks via \n-to-<br> normalisation.
• Added a new RichTextEditorWithPresets component that renders a split-panel layout: the rich-text editor on the left and a clickable preset list on the right. The preset panel is only shown when the editor is empty. Selecting a preset populates both the prompt and responseFields fields simultaneously via IPreset assignments.
• Added a containerClassName prop to RichTextEditor and an editor--borderless CSS variant to allow the editor to render without its own border when embedded inside the preset panel's shared border container.
• Exposed presets on the ActionSubstepArgument GraphQL type and IFieldRichText TypeScript interface, with new IPreset and IPresetAssignment types.
• InputCreator now renders RichTextEditorWithPresets instead of RichTextEditor when a field has presets defined.
• The hiddenIf condition for responseFields now watches the prompt field instead of the removed promptType field.

How to test?

New RTE with presets

• Presets are displayed by default when the new action is created
• Typing in the RTE removes the presets
• Selecting the preset automatically populates the RTE and clears the presets
• Clearing the RTE shows the presets again
• Presets are rendered properly i.e., with proper spacing and formatting

Sanity check

• Other actions using rich-text are rendered correctly and function correctly i.e., Postman
  • Can format text
  • Can add tables
  • Can add images
  • Can render saved parameters properly

[kevinkim-ogp]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• refactor: create RTE with presets #1558 👈 (View in Graphite)
• chore: UI improvments for sending prompt #1556
• PLU-708 (chore): design improvements #1554
• feat: add maxFiles, multirow column labels #1553
• trunk/ai-actions

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