ci(deploy): switch from Cloudflare Pages to GitHub Pages

Migrate build and deployment pipeline from Cloudflare Pages to GitHub Pages.
Adds production-ready deploy workflow in deploy-github-pages.yml with proper
artifact handling. Removes Cloudflare-specific tooling: wrangler config, _headers,
_redirects, and CSP hash injection scripts (no longer needed with GitHub Pages
static hosting). Updates package.json build scripts and all project documentation
to reflect new deployment target and simplified architecture.

web/docs/development-roadmap.md

@@ -80,7 +80,7 @@ European Bingo 90 patterns. **Out of scope** — Tân Tân uses single-line "Kin
 ## Decision Rationale
 
 All decisions follow **YAGNI** (You Aren't Gonna Need It), **KISS** (Keep It Simple), **DRY** (Don't Repeat Yourself):
-- No multiplayer sync → adds server dependency, breaks static export (Cloudflare Pages)
+- No multiplayer sync → adds server dependency, breaks static export (GitHub Pages)
 - No i18n → Vietnamese-only community, localizing adds complexity
 - Unit tests implemented → critical paths (constraints, persistence, settings) now have automated coverage
 - Component/E2E tests deferred → small codebase, manual testing sufficient for UI flows