feat: add operation and resource validation with intelligent suggestions

- Added OperationSimilarityService for validating operations with "Did you mean...?" suggestions
- Added ResourceSimilarityService for validating resources with plural/singular detection
- Implements Levenshtein distance algorithm for typo detection
- Pattern matching for common operation/resource mistakes
- 5-minute cache with automatic cleanup to prevent memory leaks
- Confidence scoring (30% minimum threshold) for suggestion quality
- Resource-aware operation filtering for contextual suggestions
- Safe JSON parsing with ValidationServiceError for proper error handling
- Type guards for safe property access
- Performance optimizations with early termination
- Comprehensive test coverage (37 new tests)
- Integration tested with n8n-mcp-tester agent

Example use cases:
- "listFiles" → suggests "search" for Google Drive
- "files" → suggests singular "file"
- "flie" → suggests "file" (typo correction)
- "downlod" → suggests "download"

🤖 Generated with Claude Code

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

src/errors/validation-service-error.ts

@@ -0,0 +1,53 @@
+/**
+ * Custom error class for validation service failures
+ */
+export class ValidationServiceError extends Error {
+  constructor(
+    message: string,
+    public readonly nodeType?: string,
+    public readonly property?: string,
+    public readonly cause?: Error
+  ) {
+    super(message);
+    this.name = 'ValidationServiceError';
+
+    // Maintains proper stack trace for where our error was thrown (only available on V8)
+    if (Error.captureStackTrace) {
+      Error.captureStackTrace(this, ValidationServiceError);
+    }
+  }
+
+  /**
+   * Create error for JSON parsing failure
+   */
+  static jsonParseError(nodeType: string, cause: Error): ValidationServiceError {
+    return new ValidationServiceError(
+      `Failed to parse JSON data for node ${nodeType}`,
+      nodeType,
+      undefined,
+      cause
+    );
+  }
+
+  /**
+   * Create error for node not found
+   */
+  static nodeNotFound(nodeType: string): ValidationServiceError {
+    return new ValidationServiceError(
+      `Node type ${nodeType} not found in repository`,
+      nodeType
+    );
+  }
+
+  /**
+   * Create error for critical data extraction failure
+   */
+  static dataExtractionError(nodeType: string, dataType: string, cause?: Error): ValidationServiceError {
+    return new ValidationServiceError(
+      `Failed to extract ${dataType} for node ${nodeType}`,
+      nodeType,
+      dataType,
+      cause
+    );
+  }
+}