Add DOM-audited HTML-to-PPTX workflow

[LearnAIHubC]

Summary

• make model-authored HTML/CSS the default creative path instead of an intermediate JSON schema
• add a Chromium DOM preflight for overflow, overlap, unexpected wrapping, centered text/icons, chart labels, and shape-aware text containment
• add a seven-slide polished composition library, editable PPTX reference, contact-sheet tooling, and refreshed README visuals
• add regression coverage for direct HTML conversion, DOM-audit failures, layout guards, multiline text, and legacy JSON compatibility

Why

The previous workflow depended too heavily on post-conversion screenshots and explicit containment/overlap guards. That made layout problems such as hidden wrapping, off-center icons, missing chart labels, and text clipping harder to catch before PPTX generation.

The new preflight validates browser geometry immediately after HTML authoring. Draft iterations can now be corrected from structured DOM errors without repeated screenshots, while one final PPTX render remains for PowerPoint-specific font and reconstruction differences.

User and developer impact

• no fixed layout enum is required for normal creative generation
• HTML remains the revision source of truth
• --dom-audit-only validates HTML without writing a PPTX
• final decks retain editable text, shapes, gradients, and icon objects
• the bundled template demonstrates the guard contract without fixing the user's content or slide sequence

Validation

• npm test
• Skill quick_validate.py
• PowerPoint canvas overflow test
• seven-slide DOM audit with 70 guard elements and zero issues
• deliberate regression fixtures for all new DOM-audit failure categories
• npm pack --dry-run --json
• installed Skill audit and smoke test