Complete 4.2.2: Form Validation Implementation

- Add form-group wrappers and error message elements to HTML
- Implement comprehensive client-side validation for nickname and message inputs
- Add visual feedback using existing CSS validation classes
- Include success confirmation states and proper error handling
- Enhance accessibility with focus management and screen reader support

UI_UPDATE.MD

@@ -465,10 +465,18 @@ All utilities follow the established pattern of using CSS custom properties from
 - [x] Implement focus indicators meeting WCAG standards
 - [x] Add active and pressed state styling
 
-#### 4.2.2: Form Validation
-- [ ] Implement visual form validation feedback
-- [ ] Add error state styling
-- [ ] Create success confirmation states
+#### 4.2.2: Form Validation - COMPLETED 9/29/2025
+- [x] Implement visual form validation feedback
+- [x] Add error state styling
+- [x] Create success confirmation states
+
+**Notes:** Comprehensive form validation system implemented for chat inputs including:
+- HTML structure updates: Added form-group wrappers with error message elements for nickname and message inputs
+- Enhanced JavaScript validation: Added client-side validation with detailed error messages for nickname (1-20 chars, alphanumeric/places) and message (1-1000 chars) requirements
+- CSS integration: Utilizes existing .form-group--error and .form-group--success classes for visual feedback
+- User experience: Error messages display below inputs, success states provide green styling and toast confirmation, focus management ensures good UX flow
+- Validation coverage: Empty inputs, character length limits, nickname character restrictions, and server error handling
+- Accessibility: Proper error messaging and focus management for screen readers and keyboard navigation
 
 ### Sub-task 4.3: Enhanced User Feedback Systems