Fix ES module/CommonJS mismatch in shared package

- Rename CommonJS build output from .js to .cjs extensions
- Add .js extensions to ESM imports (required by Node.js)
- Add .cjs extensions to CommonJS requires
- Add post-build scripts for both ESM and CommonJS builds
- Update package.json exports to reference .cjs files for require()

Fixes: ReferenceError: exports is not defined in ES module scope

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

shared/scripts/postbuild-esm.cjs

@@ -0,0 +1,30 @@
+const fs = require('fs');
+const path = require('path');
+
+// Recursively process all .js files in esm directory
+function processDirectory(dir) {
+  const files = fs.readdirSync(dir);
+  
+  files.forEach(file => {
+    const filePath = path.join(dir, file);
+    const stat = fs.statSync(filePath);
+    
+    if (stat.isDirectory()) {
+      processDirectory(filePath);
+    } else if (file.endsWith('.js')) {
+      // Read the file
+      let content = fs.readFileSync(filePath, 'utf8');
+      
+      // Replace import/export statements to add .js extension
+      // Replace from "./path" with from "./path.js" (for relative imports only)
+      content = content.replace(/from ["'](\.[^"']*?)(?<!\.js)["']/g, 'from "$1.js"');
+      
+      // Write back
+      fs.writeFileSync(filePath, content, 'utf8');
+      console.log(`✓ Updated ${filePath}`);
+    }
+  });
+}
+
+processDirectory('./dist/esm');
+console.log('✓ ESM post-build processing complete');