feat(core): add shared utilities and types

Add shared layer:
- Result<T,E> type for error handling
- BaseError and error subclasses
- Guards for runtime type checking
- Application constants

packages/core/src/shared/utils/Guards.ts

@@ -0,0 +1,44 @@
+/**
+ * Type guard utilities for runtime type checking
+ */
+export class Guards {
+    public static isNullOrUndefined(value: unknown): value is null | undefined {
+        return value === null || value === undefined;
+    }
+
+    public static isString(value: unknown): value is string {
+        return typeof value === 'string';
+    }
+
+    public static isNumber(value: unknown): value is number {
+        return typeof value === 'number' && !isNaN(value);
+    }
+
+    public static isBoolean(value: unknown): value is boolean {
+        return typeof value === 'boolean';
+    }
+
+    public static isObject(value: unknown): value is object {
+        return typeof value === 'object' && value !== null && !Array.isArray(value);
+    }
+
+    public static isArray<T>(value: unknown): value is T[] {
+        return Array.isArray(value);
+    }
+
+    public static isEmpty(value: string | unknown[] | object | null | undefined): boolean {
+        if (Guards.isNullOrUndefined(value)) {
+            return true;
+        }
+
+        if (Guards.isString(value) || Guards.isArray(value)) {
+            return value.length === 0;
+        }
+
+        if (Guards.isObject(value)) {
+            return Object.keys(value).length === 0;
+        }
+
+        return false;
+    }
+}