Generate an academic slide deck specification from existing structured empirical outputs.

Use this after research_brief, baseline econometrics, and optionally heterogeneity/paper draft artifacts already exist.

Outputs:
- `slides.md`
- `slides.json`
- `speaker_notes.md`
- `slide_asset_manifest.json`

Rules:
- Default to a grounded 8-12 slide academic seminar structure.
- Reuse existing tables and figures when available.
- If no suitable chart exists, recommend a visual instead of inventing one.
