refactor: fix biome linting issues and update project documentation

- Fix 36+ biome linting issues reducing errors/warnings from 227 to 191
- Replace explicit 'any' types with proper TypeScript interfaces
- Fix React hooks dependencies and useCallback patterns
- Resolve unused variables and parameter assignment issues
- Improve accessibility with proper label associations
- Add comprehensive API documentation for admin and security features
- Update README.md with accurate PostgreSQL setup and current tech stack
- Create complete documentation for audit logging, CSP monitoring, and batch processing
- Fix outdated project information and missing developer workflows

app/api/platform/companies/[id]/users/route.ts

@@ -73,14 +73,13 @@ export async function POST(
           { error: "User already exists in this company" },
           { status: 400 }
         );
-      } else {
-        return NextResponse.json(
-          {
-            error: `Email already in use by a user in company: ${existingUser.company.name}. Each email address can only be used once across all companies.`
-          },
-          { status: 400 }
-        );
       }
+      return NextResponse.json(
+        {
+          error: `Email already in use by a user in company: ${existingUser.company.name}. Each email address can only be used once across all companies.`,
+        },
+        { status: 400 }
+      );
     }
 
     // Generate a temporary password (in a real app, you'd send an invitation email)