feat: implement mass balance validation for Story 7.1

- Added port_mass_flows to Component trait and implements for core components.
- Added System::check_mass_balance and integrated it into the solver.
- Restored connect methods for ExpansionValve, Compressor, and Pipe to fix integration tests.
- Updated Python and C bindings for validation errors.
- Updated sprint status and story documentation.

bindings/wasm/tests/simple_cycle.js

@@ -0,0 +1,44 @@
+const { default: init, version, list_available_fluids, WasmSystem, WasmPressure, WasmTemperature, WasmFallbackConfig } = require('../pkg/entropyk_wasm.js');
+
+async function main() {
+    // Initialize WASM module
+    await init();
+    
+    console.log('Entropyk WASM Test');
+    console.log('===================');
+    console.log('Version:', version());
+    
+    // Test fluid listing
+    const fluids = list_available_fluids();
+    console.log('Available fluids:', fluids);
+    
+    // Test pressure creation
+    const p = new WasmPressure(101325.0);
+    console.log('Pressure (Pa):', p.pascals());
+    console.log('Pressure (bar):', p.bar());
+    
+    // Test temperature creation
+    const t = WasmTemperature.from_celsius(25.0);
+    console.log('Temperature (K):', t.kelvin());
+    console.log('Temperature (°C):', t.celsius());
+    
+    // Test system creation
+    const system = new WasmSystem();
+    console.log('System created');
+    console.log('Node count:', system.node_count());
+    console.log('Edge count:', system.edge_count());
+    
+    // Test solver configuration
+    const config = new WasmFallbackConfig();
+    config.timeout_ms(1000);
+    
+    // Test JSON output
+    console.log('System JSON:', system.toJson());
+    
+    console.log('\nAll tests passed!');
+}
+
+main().catch(err => {
+    console.error('Test failed:', err);
+    process.exit(1);
+});