[puppeteer] Show export size summary before generating code

[S1mplector]

Module: Puppeteer

Goal:
Before export/register actions, show creators a compact summary of the generated timeline size and affected scene objects.

Acceptance criteria:

• Confirmation popup includes generated line count, action count, track count, duration, and affected characters/layers.
• Summary distinguishes metadata comments from executable script actions.
• Large exports call out likely editor/runtime cost.
• Tests cover summary generation from a representative project.

Notes:
This complements the existing detailed registration/export confirmation flow.