feat: add agent-oriented slide-gen CLI example

[yangluoshen]

Summary

• add a slide-gen-cli teaching example for agent-authored multi-page Univer presentations built through SVG compile
• keep task-scoped authoring sources, API references, Worktree review, native chart/table enhancements, and PPTX export
• add an online viewer with Files/Worktrees tabs, newest-first ordering, in-place Slide switching, and the authorized development license

Validation

• pnpm check in examples/slide-gen-cli
• 4 test files and 9 tests passed
• browser acceptance covered multi-page generation, Worktree review, in-place navigation, and licensed rendering