chore: remove Replit/homegit references for public GitHub repo

- Simplify dev script (drop Replit-specific env vars)
- Remove REPLIT_* fallbacks from scripts/build.js
- Rewrite root README for GitHub (local build, no EAS, no homegit URLs)
- Update clone URL in artifacts README → GitHub
- Remove replit.md (Replit workspace descriptor, no longer needed)
- Untrack scripts/push-to-gitea.sh (internal-only, added to .gitignore)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -47,3 +47,4 @@ Thumbs.db
 # Replit
 .cache/
 .local/
+scripts/push-to-gitea.sh