Improve code-editing guidance in tutorials

Problem

• Current tutorials rely mainly on Tutorial Copilot text instructions, so users need to infer which code to delete, change, or add from written descriptions.
• For first-time users, text-only guidance is not direct enough and can lead to misunderstanding.
• If Copilot intervenes too heavily, it weakens the experience of completing the tutorial independently.

What Needs Improvement

• Keep Copilot as a behind-the-scenes assistant in tutorials, providing prompts only when users cannot proceed.
• Limit API Reference to the APIs used in the current tutorial.
• Remove drag guidance (code-drag-hint).
• Keep code-editing guidance (code-delete-hint, code-change-hint).
• Compare diffs at the full-phrase level, not at the individual-character level.

Expected Outcome

• Users can more clearly understand which code to edit and how to edit it.
• Tutorial guidance becomes more direct without feeling overly hand-held.

Acceptance Criteria

• API Reference only shows APIs relevant to the current tutorial.
• Drag guidance (code-drag-hint) is removed.
• Diff comparison is shown at the full-phrase level.
• Copilot does not over-intervene when users can proceed independently.

Locate the tutorial code that controls Tutorial Copilot prompts, API Reference filtering, code-drag-hint, code-delete-hint, code-change-hint, and diff comparison. Trace how these controls are used in a tutorial, then verify that only relevant APIs appear, drag guidance is absent, full phrases are compared, and Copilot stays behind the scenes when users can proceed independently.