Add initial documentation and test placeholders

- Comprehensive README.md with run instructions
- Backend test structure (server.test.js)
- Frontend test structure (App.test.js)
- Setup instructions and troubleshooting guide
- API documentation and project structure overview

backend/tests/server.test.js

@@ -0,0 +1,42 @@
+/**
+ * Placeholder test file for Line of Sight Backend
+ * 
+ * TODO: Add real tests for:
+ * - API endpoint validation
+ * - Geospatial calculations
+ * - Database queries
+ * - Error handling
+ */
+
+describe('Line of Sight Backend', () => {
+  describe('GET /api/health', () => {
+    test('should return 200 OK', () => {
+      // TODO: Implement health check test
+      expect(true).toBe(true);
+    });
+  });
+
+  describe('GET /api/line-of-sight', () => {
+    test('should return valid response structure', () => {
+      // TODO: Implement line of sight API test
+      expect(true).toBe(true);
+    });
+
+    test('should handle missing parameters', () => {
+      // TODO: Implement error handling test
+      expect(true).toBe(true);
+    });
+  });
+
+  describe('Geospatial Calculations', () => {
+    test('should calculate great circle path', () => {
+      // TODO: Implement geospatial calculation tests
+      expect(true).toBe(true);
+    });
+
+    test('should filter cities within tolerance', () => {
+      // TODO: Implement tolerance filtering tests
+      expect(true).toBe(true);
+    });
+  });
+});