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>

artifacts/postiz-mobile/package.json

@@ -4,7 +4,7 @@
   "private": true,
   "main": "expo-router/entry",
   "scripts": {
-    "dev": "EXPO_PACKAGER_PROXY_URL=https://$REPLIT_EXPO_DEV_DOMAIN EXPO_PUBLIC_DOMAIN=$REPLIT_DEV_DOMAIN EXPO_PUBLIC_REPL_ID=$REPL_ID REACT_NATIVE_PACKAGER_HOSTNAME=$REPLIT_DEV_DOMAIN pnpm exec expo start --localhost --port $PORT",
+    "dev": "pnpm exec expo start",
     "build": "node scripts/build.js",
     "serve": "node server/serve.js",
     "typecheck": "tsc -p tsconfig.json --noEmit",