feat: implement comprehensive AI node validation (Phase 1)

Implements AI-specific validation for n8n workflows based on
docs/FINAL_AI_VALIDATION_SPEC.md

## New Features

### AI Tool Validators (src/services/ai-tool-validators.ts)
- 13 specialized validators for AI tool sub-nodes
  - HTTP Request Tool: 6 validation checks
  - Code Tool: 7 validation checks
  - Vector Store Tool: 7 validation checks
  - Workflow Tool: 5 validation checks
  - AI Agent Tool: 7 validation checks
  - MCP Client Tool: 4 validation checks
  - Calculator & Think tools: description validation
  - 4 Search tools: credentials + description validation

### AI Node Validator (src/services/ai-node-validator.ts)
- `buildReverseConnectionMap()` - Critical utility for AI connections
- `validateAIAgent()` - 8 comprehensive checks including:
  - Language model connections (1 or 2 if fallback)
  - Output parser validation
  - Prompt type configuration
  - Streaming mode constraints (CRITICAL)
  - Memory connections
  - Tool connections
  - maxIterations validation
- `validateChatTrigger()` - Streaming mode constraint validation
- `validateBasicLLMChain()` - Simple chain validation
- `validateAISpecificNodes()` - Main validation entry point

### Integration (src/services/workflow-validator.ts)
- Seamless integration with existing workflow validation
- Performance-optimized (only runs when AI nodes present)
- Type-safe conversion of validation issues

## Key Architectural Decisions

1. **Reverse Connection Mapping**: AI connections flow TO consumer nodes
   (reversed from standard n8n pattern). Built custom mapping utility.

2. **Streaming Mode Validation**: AI Agent with streaming MUST NOT have
   main output connections - responses stream back through Chat Trigger.

3. **Modular Design**: Separate validators for tools vs nodes for
   maintainability and testability.

## Code Quality

- TypeScript: Clean compilation, strong typing
- Code Review Score: A- (90/100)
- No critical bugs or security issues
- Comprehensive error messages with codes
- Well-documented with spec references

## Testing Status

- Build: ✅ Passing
- Type Check: ✅ No errors
- Unit Tests: Pending (Phase 5)
- Integration Tests: Pending (Phase 5)

## Documentation

- Moved FINAL_AI_VALIDATION_SPEC.md to docs/
- Inline comments reference spec line numbers
- Clear function documentation

## Next Steps

1. Address code review Priority 1 fixes
2. Add comprehensive unit tests (Phase 5)
3. Create AI Agents guide (Phase 4)
4. Enhance search_nodes with AI examples (Phase 3)

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

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

src/services/workflow-validator.ts

@@ -10,6 +10,7 @@ import { ExpressionFormatValidator } from './expression-format-validator';
 import { NodeSimilarityService, NodeSuggestion } from './node-similarity-service';
 import { NodeTypeNormalizer } from '../utils/node-type-normalizer';
 import { Logger } from '../utils/logger';
+import { validateAISpecificNodes, hasAINodes } from './ai-node-validator';
 const logger = new Logger({ prefix: '[WorkflowValidator]' });
 
 interface WorkflowNode {
@@ -174,9 +175,30 @@ export class WorkflowValidator {
           this.checkWorkflowPatterns(workflow, result, profile);
         }
 
+        // Validate AI-specific nodes (AI Agent, Chat Trigger, AI tools)
+        if (workflow.nodes.length > 0 && hasAINodes(workflow)) {
+          const aiIssues = validateAISpecificNodes(workflow);
+          // Convert AI validation issues to workflow validation format
+          for (const issue of aiIssues) {
+            const validationIssue: ValidationIssue = {
+              type: issue.severity === 'error' ? 'error' : 'warning',
+              nodeId: issue.nodeId,
+              nodeName: issue.nodeName,
+              message: issue.message,
+              details: issue.code ? { code: issue.code } : undefined
+            };
+
+            if (issue.severity === 'error') {
+              result.errors.push(validationIssue);
+            } else {
+              result.warnings.push(validationIssue);
+            }
+          }
+        }
+
         // Add suggestions based on findings
         this.generateSuggestions(workflow, result);
-        
+
         // Add AI-specific recovery suggestions if there are errors
         if (result.errors.length > 0) {
           this.addErrorRecoverySuggestions(result);