enhance: Add HTTP Request node validation suggestions (issue #361)

Added helpful suggestions for HTTP Request node best practices after thorough investigation of issue #361.

## What's New

1. **alwaysOutputData Suggestion**
   - Suggests adding alwaysOutputData: true at node level
   - Prevents silent workflow failures when HTTP requests error
   - Ensures downstream error handling can process failed requests

2. **responseFormat Suggestion for API Endpoints**
   - Suggests setting options.response.response.responseFormat
   - Prevents JSON parsing confusion
   - Triggered for URLs containing /api, /rest, supabase, firebase, googleapis, .com/v

3. **Enhanced URL Protocol Validation**
   - Detects missing protocol in expression-based URLs
   - Warns about patterns like =www.{{ $json.domain }}.com
   - Warns about expressions without protocol

## Investigation Findings

**Key Discoveries:**
- Mixed expression syntax =literal{{ expression }} actually works in n8n (claim was incorrect)
- Real validation gaps: missing alwaysOutputData and responseFormat checks
- Compared broken vs fixed workflows to identify actual production issues

**Testing Evidence:**
- Analyzed workflow SwjKJsJhe8OsYfBk with mixed syntax - executions successful
- Compared broken workflow (mBmkyj460i5rYTG4) with fixed workflow (hQI9pby3nSFtk4TV)
- Identified that fixed workflow has alwaysOutputData: true and explicit responseFormat

## Impact

- Non-Breaking: All changes are suggestions/warnings, not errors
- Actionable: Clear guidance on how to implement best practices
- Production-Focused: Addresses real workflow reliability concerns

## Test Coverage

Added 8 new test cases covering:
- alwaysOutputData suggestion for all HTTP Request nodes
- responseFormat suggestion for API endpoint detection
- responseFormat NOT suggested when already configured
- URL protocol validation for expression-based URLs
- No false positives when protocol is correctly included

## Files Changed

- src/services/enhanced-config-validator.ts - Added enhanceHttpRequestValidation()
- tests/unit/services/enhanced-config-validator.test.ts - Added 8 test cases
- CHANGELOG.md - Documented enhancement with investigation findings
- package.json - Bump version to 2.22.2

Fixes #361

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

src/services/enhanced-config-validator.ts

@@ -401,7 +401,48 @@ export class EnhancedConfigValidator extends ConfigValidator {
     config: Record<string, any>,
     result: EnhancedValidationResult
   ): void {
-    // Examples removed - validation provides error messages and fixes instead
+    const url = String(config.url || '');
+    const options = config.options || {};
+
+    // 1. Suggest alwaysOutputData for better error handling (node-level property)
+    // Note: We can't check if it exists (it's node-level, not in parameters),
+    // but we can suggest it as a best practice
+    if (!result.suggestions.some(s => typeof s === 'string' && s.includes('alwaysOutputData'))) {
+      result.suggestions.push(
+        'Consider adding alwaysOutputData: true at node level (not in parameters) for better error handling. ' +
+        'This ensures the node produces output even when HTTP requests fail, allowing downstream error handling.'
+      );
+    }
+
+    // 2. Suggest responseFormat for API endpoints
+    const isApiEndpoint = url.includes('/api') || url.includes('/rest') ||
+                          url.includes('supabase') || url.includes('firebase') ||
+                          url.includes('googleapis') || url.includes('.com/v');
+
+    if (isApiEndpoint && !options.response?.response?.responseFormat) {
+      result.suggestions.push(
+        'API endpoints should explicitly set options.response.response.responseFormat to "json" or "text" ' +
+        'to prevent confusion about response parsing. Example: ' +
+        '{ "options": { "response": { "response": { "responseFormat": "json" } } } }'
+      );
+    }
+
+    // 3. Enhanced URL protocol validation for expressions
+    if (url && url.startsWith('=')) {
+      // Expression-based URL - check for common protocol issues
+      const expressionContent = url.slice(1); // Remove = prefix
+
+      // Check for missing protocol in expression
+      if (expressionContent.startsWith('www.') ||
+          (expressionContent.includes('{{') && !expressionContent.includes('http'))) {
+        result.warnings.push({
+          type: 'invalid_value',
+          property: 'url',
+          message: 'URL expression appears to be missing http:// or https:// protocol',
+          suggestion: 'Include protocol in your expression. Example: ={{ "https://" + $json.domain + ".com" }}'
+        });
+      }
+    }
   }
   
   /**