feat(export): PPTX fidelity upgrade - content-parity gate, OOXML verifier, SVG exporters

[tph-kds]

Summary

Adds a fidelity layer to the PPTX export pipeline that ensures meaningful visible content survives into the PowerPoint output - no diagram summaries, no silent omissions, a blocking content-parity gate, and real OOXML archive verification.

What's included

Fidelity layer (new modules)

• fidelity-types.ts - FidelityBlockReport, PptxFidelityPolicy, FidelityHardRules
• fidelity-policy.ts - default policy with 0.9 meaningful-content recall threshold
• content-parity.ts - text-recall metric (ratio of exported text tokens to expected)
• representation-planner.ts - per-block representation planning (native/svg/raster/unsupported)
• fidelity-report.ts - report builder, status mapping, block counting

SVG generators

• svg-diagram.ts - deterministic Mermaid-free diagram SVG generator
• svg-snapshot.ts - structured SVG snapshot fallback for visual blocks

OOXML structural verifier

• pptx-verifier.ts - JSZip-based archive validation (slides, text survival, media rels, notes, links)

Exporter wiring

• pptx-exporter.ts: fidelity-first mode, per-block representation, parity gate, archive verification
• block-exporters/video.ts: new video exporter with SVG snapshot fallback
• block-exporters/diagram.ts: SVG via renderDiagramSvg
• block-exporters/fallback.ts: SVG snapshot fallback

Preflight and dialog

• export-preflight.ts: estimated recall, fallbacks, missing blocks
• export-dialog.tsx: fidelity-first mode selector, preflight summary, blocks download when recall < 0.9

Starter-components mirror

• Adapted imports for scaffold's module structure
• Block type alias added to deck-types.ts
• Full fidelity tree, video, and pptx-verifier

Bug fixes

• Fixed pptx-theme.ts: removed invalid headColor/bodyColor (PptxGenJS ThemeProps only supports fonts)
• Eliminated double calculateContentParity iteration in buildExportReport

Tests

• 24 test files, 234 tests all passing

Documentation

• Updated deckforge-export SKILL.md, system-prompt.md, workflows
• Added QUICKSTART.md for new users

Validation

• 234 tests pass (vitest)
• Typecheck clean
• npm run validate exit 0
• All 7 skill bundles PASS

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