Add LinkedIn carousel for v2.4 (Two-Stage DiD)

[igerber]

Summary

• Add 10-slide LinkedIn carousel PDF for the v2.4 release featuring Two-Stage DiD (Gardner 2022)
• New standalone generator script (carousel/generate_v24_pdf.py) adapted from the v2.3 template
• LaTeX-rendered equations via matplotlib with Computer Modern font for the math slide
• Teal accent color (#0891b2) replacing v2.3's amber
• Slides: hook, recap, TWFE problem diagram, two-stage procedure, math equations, honest SEs comparison, per-observation effects table, code example, full 5x2 toolkit grid, CTA

Methodology references (required if estimator / math changes)

• Method name(s): N/A - no methodology changes (carousel/marketing assets only)
• Paper / source link(s): N/A
• Any intentional deviations from the source (and why): None

Validation

• Tests added/updated: No test changes (marketing asset, not library code)
• Backtest / simulation / notebook evidence (if applicable): N/A

Security / privacy

• Confirm no secrets/PII in this PR: Yes

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Generated with Claude Code

[github-actions]

Overall assessment: ⚠️ Needs changes

Executive Summary

• Cross-checked TwoStageDiD slide content against docs/methodology/REGISTRY.md and diff_diff/two_stage.py; the only mismatch is variance/SE wording that overstates guarantees.
• Slide 6’s “correct coverage / GMM gets it right” language is stronger than the asymptotic GMM sandwich described in the registry.
• Minor reliability improvement: ensure temporary equation images are cleaned up even if PDF generation errors.

Methodology
Affected methods: TwoStageDiD (variance/SE messaging), references to TWFE and ImputationDiD.

• P1 — Impact: Slide 6 labels the GMM sandwich as “correct coverage” and claims “GMM gets it right,” which overstates the asymptotic sandwich variance described in the registry (no finite‑sample adjustment) and could mislead readers into assuming guaranteed coverage. Fix: soften to “asymptotically valid coverage” or “accounts for Stage 1 uncertainty,” and remove the absolute “gets it right” phrasing. (carousel/generate_v24_pdf.py:L599-L684)

Code Quality

• P3 — Impact: Temporary equation PNGs can be left behind if generation fails before cleanup() runs. Fix: wrap the body of main() in try/finally (or use a context manager) to always call cleanup(). (carousel/generate_v24_pdf.py:L932-L950)

Performance
No findings.

Maintainability
No findings.

Tech Debt
No findings.

Security
No findings.

Documentation/Tests
No findings.