fix(build): fail build if critical files are missing in dist

- Updates `scripts/build-dist.mjs` to exit with error code 1 if source files like `_redirects` or `_headers` are missing.
- Prevents silent failures where `dist` directory is incomplete, potentially causing Netlify deployment checks to fail ambiguously.
- Ensures `build:css` failure also terminates the build process explicitly.

Co-authored-by: PR0M3TH3AN <[email protected]>

scripts/build-dist.mjs

@@ -38,7 +38,8 @@ function copyFile(src, dest) {
   if (fs.existsSync(src)) {
     fs.copyFileSync(src, dest);
   } else {
-    console.warn(`Warning: Source file ${src} does not exist.`);
+    console.error(`Error: Source file ${src} does not exist.`);
+    process.exit(1);
   }
 }