feat: add the general PPTX-to-video workflow

[LingAo Xiao (ArmandXiao)]

Summary

• embed a lean general-purpose ppt2video sub-skill under paper2video; the sub-skill contains only its required SKILL.md and reuses the parent deterministic renderer
• add the editable PPTX protocol with compact Alt Text, shape-OOXML script provenance, Notes/Alt Text conflict resolution, spatial generated order, native Animation Pane timing, and script-scoped Spotlight cues
• render bottom-band subtitles from exact Edge word boundaries and enforce animation, subtitle, timeline, source-hash, and media checks in strict QA

Validation

• paper2video and ppt2video skill schema validation passed
• direct render entrypoint smoke check passed
• fresh end-to-end bundle strict QA: PASS, 0 errors, 0 warnings

Open-source hygiene

• reduced the PR to 15 core skill, protocol-reference, and renderer files
• excluded all tests, agents metadata, app builders, installers, launchers, setup wrappers, duplicate repository discovery files, generated media, reports, caches, demos, and unrelated worktree changes
• scanned the final single-commit diff for credentials, private keys, tokens, internal absolute paths, attachment paths, and user-specific workspace paths

[LingAo Xiao (ArmandXiao)]

Superseded by #43, which carries this editable PPTX workflow forward as a standalone pptx2video package and leaves Paper2Video with installation and public-CLI bridge instructions. Closing this PR in favor of the consolidated extraction.