docs: reflect real posterior-draw architecture in AGENTS/README/HANDOFF

- AGENTS.md: Replace §4 (API Endpoint Availability) with updated text; insert
  new §5 (Real posterior draws via duckdb-wasm) documenting the shift from
  synthetic normal-approximation draws to client-side fetches via duckdb-wasm
  against the public Hugging Face parquet dataset. Include actual payload size
  (~39MB uncompressed / ~8.86MB gzipped). Renumber subsequent items.
- README.md: Update Chart 5 description in "What It Does" to reflect real draws
  + fallback behavior. Update API table to clarify that /api/v1/draws is not
  called from app but informs the Hugging Face URL the app fetches directly.
- HANDOFF.md: Mark "Raw posterior draws" as done (2026-08-11) with reference
  to the design spec.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

HANDOFF.md

@@ -33,7 +33,7 @@ The CORS proxy fallback code (`proxy.php`, nginx reverse proxy config, `VITE_PRO
 ## What Needs to Be Done Next
 
 ### Future Enhancements
-- **Raw posterior draws**: The `/api/v1/draws?...` endpoint returns Parquet shard URLs for bulk processing, not browser-friendly draw data. If actual posterior distributions are needed in Chart 5 (instead of synthetic normal approximation), a new API endpoint would be required.
+- ~~**Raw posterior draws**~~ — Done (2026-08-11). Charts 2 and 3 now fetch real posterior draws client-side via `@duckdb/duckdb-wasm` against the public Hugging Face parquet dataset. See `docs/superpowers/specs/2026-08-11-empirical-draws-wasm-design.md`.
 - **Automated testing**: No test suite exists; consider adding basic tests for chart rendering and API error handling.
 
 ## Key Files