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/src/components.rs

@@ -0,0 +1,150 @@
+//! WASM component bindings (stub).
+//!
+//! Provides JavaScript-friendly wrappers for thermodynamic components.
+//! NOTE: This is a minimal implementation to demonstrate the WASM build.
+//! Full component bindings require additional development.
+
+use crate::types::{WasmEnthalpy, WasmMassFlow, WasmPressure, WasmTemperature};
+use serde::Serialize;
+use wasm_bindgen::prelude::*;
+
+/// WASM wrapper for Compressor component (stub).
+#[wasm_bindgen]
+pub struct WasmCompressor {
+    _fluid: String,
+}
+
+#[wasm_bindgen]
+impl WasmCompressor {
+    /// Create a new compressor.
+    #[wasm_bindgen(constructor)]
+    pub fn new(fluid: String) -> Result<WasmCompressor, JsValue> {
+        Ok(WasmCompressor { _fluid: fluid })
+    }
+
+    /// Get component name.
+    pub fn name(&self) -> String {
+        "Compressor".to_string()
+    }
+}
+
+/// WASM wrapper for Condenser component (stub).
+#[wasm_bindgen]
+pub struct WasmCondenser {
+    _fluid: String,
+    _ua: f64,
+}
+
+#[wasm_bindgen]
+impl WasmCondenser {
+    /// Create a new condenser.
+    #[wasm_bindgen(constructor)]
+    pub fn new(fluid: String, ua: f64) -> Result<WasmCondenser, JsValue> {
+        Ok(WasmCondenser {
+            _fluid: fluid,
+            _ua: ua,
+        })
+    }
+
+    /// Get component name.
+    pub fn name(&self) -> String {
+        "Condenser".to_string()
+    }
+}
+
+/// WASM wrapper for Evaporator component (stub).
+#[wasm_bindgen]
+pub struct WasmEvaporator {
+    _fluid: String,
+    _ua: f64,
+}
+
+#[wasm_bindgen]
+impl WasmEvaporator {
+    /// Create a new evaporator.
+    #[wasm_bindgen(constructor)]
+    pub fn new(fluid: String, ua: f64) -> Result<WasmEvaporator, JsValue> {
+        Ok(WasmEvaporator {
+            _fluid: fluid,
+            _ua: ua,
+        })
+    }
+
+    /// Get component name.
+    pub fn name(&self) -> String {
+        "Evaporator".to_string()
+    }
+}
+
+/// WASM wrapper for ExpansionValve component (stub).
+#[wasm_bindgen]
+pub struct WasmExpansionValve {
+    _fluid: String,
+}
+
+#[wasm_bindgen]
+impl WasmExpansionValve {
+    /// Create a new expansion valve.
+    #[wasm_bindgen(constructor)]
+    pub fn new(fluid: String) -> Result<WasmExpansionValve, JsValue> {
+        Ok(WasmExpansionValve { _fluid: fluid })
+    }
+
+    /// Get component name.
+    pub fn name(&self) -> String {
+        "ExpansionValve".to_string()
+    }
+}
+
+/// WASM wrapper for Economizer component (stub).
+#[wasm_bindgen]
+pub struct WasmEconomizer {
+    _fluid: String,
+    _ua: f64,
+}
+
+#[wasm_bindgen]
+impl WasmEconomizer {
+    /// Create a new economizer.
+    #[wasm_bindgen(constructor)]
+    pub fn new(fluid: String, ua: f64) -> Result<WasmEconomizer, JsValue> {
+        Ok(WasmEconomizer {
+            _fluid: fluid,
+            _ua: ua,
+        })
+    }
+
+    /// Get component name.
+    pub fn name(&self) -> String {
+        "Economizer".to_string()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[wasm_bindgen_test]
+    fn test_compressor_creation() {
+        let compressor = WasmCompressor::new("R134a".to_string());
+        assert!(compressor.is_ok());
+    }
+
+    #[wasm_bindgen_test]
+    fn test_condenser_creation() {
+        let condenser = WasmCondenser::new("R134a".to_string(), 1000.0);
+        assert!(condenser.is_ok());
+    }
+
+    #[wasm_bindgen_test]
+    fn test_evaporator_creation() {
+        let evaporator = WasmEvaporator::new("R134a".to_string(), 800.0);
+        assert!(evaporator.is_ok());
+    }
+
+    #[wasm_bindgen_test]
+    fn test_expansion_valve_creation() {
+        let valve = WasmExpansionValve::new("R134a".to_string());
+        assert!(valve.is_ok());
+    }
+}