feat: Ability to create and place content via Gutenberg API

[Stefan0x]

What does this PR do?

Adds a new content-generate ability that fills a Gutenberg page with AI-generated block content. The ability makes a separate streaming LLM call (via the loaded WebLLM/external engine) to generate a JSON array of Gutenberg block definitions, then converts them to real blocks using wp.blocks.createBlock() and inserts them into the editor via wp.data.dispatch('core/block-editor').resetBlocks().

Includes robust JSON parsing that handles Qwen 3 tags, truncated responses, and malformed array output (],[ normalization). Falls back to a structured template when no model is loaded or the output format fails.

When used outside the editor, it should return a navigation message "hint" without calling the LLM. (WIP)

Type

• New ability
• New workflow
• Bug fix
• Enhancement
• Docs

How to test

1. Navigate to any page/post in the block editor (e.g. wp-admin/post.php?post=1&action=edit)
2. Open the AI Assistant sidebar
3. Type "fill this page with content about how to cook pancakes"
4. Confirm the action when prompted
5. Verify that AI-generated blocks (headings, paragraphs, lists) appear in the editor
6. Verify you can undo with Ctrl+Z / Cmd+Z
7. Navigate to the main WP Admin dashboard and try the same command — verify you get an instant "navigate to the
   editor" message without any loading delay
8. If no AI model is loaded, verify that a placeholder template is inserted with a note to customize