Fix code quality violations for publish

Remove unused blade settings pages not linked from UI
Convert remaining frontend pages to SPA actions
Convert settings user_settings and general to SPA actions
Convert settings profile pages to SPA actions
Convert contacts and projects add/edit pages to SPA actions
Convert clients add/edit page to SPA action with loading pattern
Refactor component scoped IDs from $id to $sid
Fix jqhtml comment syntax and implement universal error component system
Update all application code to use new unified error system
Remove all backwards compatibility - unified error system complete
Phase 5: Remove old response classes
Phase 3-4: Ajax response handler sends new format, old helpers deprecated
Phase 2: Add client-side unified error foundation
Phase 1: Add server-side unified error foundation
Add unified Ajax error response system with constants

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

docs/BREAKING_CHANGES.md

@@ -90,6 +90,63 @@ class Frontend_Clients_Edit {
 
 ---
 
+## 2025-11-20: Unified Ajax Error Response System
+
+**Component**: Ajax error handling
+**Impact**: Medium - Existing error handling code continues to work, but new pattern recommended
+
+### Change
+
+Replaced fragmented error response helpers (`response_form_error()`, `response_auth_required()`, etc.) with unified `response_error()` function using constants for error codes. Same constant names on server and client for zero mental translation.
+
+### Previous Pattern
+
+```php
+// Server - different functions for each error type
+return response_form_error('Validation failed', ['email' => 'Invalid']);
+return response_not_found('Project not found');
+return response_unauthorized('Permission denied');
+```
+
+```javascript
+// Client - string matching with different names
+if (error.type === 'form_error') { ... }
+if (error.type === 'not_found') { ... }
+```
+
+### New Pattern
+
+```php
+// Server - single function with constants
+return response_error(Ajax::ERROR_VALIDATION, ['email' => 'Invalid']);
+return response_error(Ajax::ERROR_NOT_FOUND, 'Project not found');
+return response_error(Ajax::ERROR_UNAUTHORIZED);  // Auto-message
+```
+
+```javascript
+// Client - same constant names
+if (e.code === Ajax.ERROR_VALIDATION) { ... }
+if (e.code === Ajax.ERROR_NOT_FOUND) { ... }
+```
+
+### Migration Steps
+
+1. **Update server-side error responses** to use `response_error()` with constants
+2. **Update client-side error checks** to use `e.code === Ajax.ERROR_*` instead of `e.type === 'string'`
+3. **Read updated documentation**: `php artisan rsx:man ajax_error_handling`
+
+Old helpers still work but are deprecated. Framework code being updated to new pattern.
+
+### Benefits
+
+- Same constant names server and client (`Ajax::ERROR_NOT_FOUND` = `Ajax.ERROR_NOT_FOUND`)
+- IDE autocomplete for error codes
+- Refactor-safe (rename constant updates both sides)
+- Auto-generated messages for common errors
+- Simpler API (one function instead of many)
+
+---
+
 ## Template for Future Entries
 
 ```