Add programmatic GitHub Pages website for 2026 FIFA World Cup measles risk

[Copilot]

Adds a standalone interactive website visualizing simulated measles outbreak risk across the 11 FIFA 2026 host cities, deployed via GitHub Actions to GitHub Pages.

New files

• docs/index.html — Single-file website with:
  • Full-viewport Leaflet map; circles sized by P(≥10 cases), colored by MMR coverage using a color-blind-safe palette (Okabe-Ito: sky blue / orange / vermilion)
  • Popup per city with vacc rate, population, and P(≥10/20/50 cases)
  • Sortable data table, About section, and Report-an-Error block (GitHub Issues + obfuscated mailto:)
• docs/generate_data.py — Reads the same sources as README.qmd at deploy time and writes docs/data.js:
  • scenarios/<City>_outbreak_size.csv → computes P(outbreak ≥ N) at max(date) across 200 sims
  • data/mmr.csv + data/population.csv for vaccination rates and population
• docs/data.js — Committed snapshot from current CSVs so the site is locally browsable without running the script
• .github/workflows/publish_website.yml — workflow_dispatch-only workflow; runs generate_data.py then deploys docs/ to GitHub Pages via actions/deploy-pages

Data flow

scenarios/*_outbreak_size.csv  ─┐
data/mmr.csv                    ├─► generate_data.py ─► docs/data.js ─► index.html (Leaflet map)
data/population.csv            ─┘

The deploy step regenerates data.js fresh from whatever scenario CSVs are in the repo at the time, keeping the website in sync with the same data pipeline that drives the README.