chore: address PR #91 review comments

- Use StandardCharsets.UTF_8 in InputStreamReader for consistent decoding
- Extract shellCommand() helper in tests to remove OS-detection duplication

Author: orpiske

capabilities-common/src/main/java/ai/wanaku/capabilities/sdk/common/ProcessRunner.java

@@ -4,6 +4,7 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
 import java.util.Map;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -42,7 +43,8 @@ public static String runWithOutput(String... command) {
     }
 
     private static String readOutput(Process process) throws IOException {
-        try (BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()))) {
+        try (BufferedReader reader =
+                new BufferedReader(new InputStreamReader(process.getInputStream(), StandardCharsets.UTF_8))) {
             StringBuilder output = new StringBuilder();
             String line;
             while ((line = reader.readLine()) != null) {

capabilities-common/src/test/java/ai/wanaku/capabilities/sdk/common/ProcessRunnerTest.java

@@ -8,18 +8,17 @@
 
 public class ProcessRunnerTest {
 
-    private static boolean isWindows() {
-        return System.getProperty("os.name").toLowerCase().contains("win");
+    private static String[] shellCommand(String script) {
+        if (System.getProperty("os.name").toLowerCase().contains("win")) {
+            return new String[] {"cmd.exe", "/c", script};
+        } else {
+            return new String[] {"sh", "-c", script};
+        }
     }
 
     @Test
     void runWithOutput_returnsCommandOutput() {
-        String output;
-        if (isWindows()) {
-            output = ProcessRunner.runWithOutput("cmd.exe", "/c", "echo hello");
-        } else {
-            output = ProcessRunner.runWithOutput("sh", "-c", "echo hello");
-        }
+        String output = ProcessRunner.runWithOutput(shellCommand("echo hello"));
 
         assertNotNull(output, "Output should not be null");
         assertFalse(output.isEmpty(), "Output should not be empty");
@@ -28,25 +27,16 @@ void runWithOutput_returnsCommandOutput() {
 
     @Test
     void runWithOutput_nonZeroExitDoesNotThrow() {
-        String output;
-        if (isWindows()) {
-            output = assertDoesNotThrow(() -> ProcessRunner.runWithOutput("cmd.exe", "/c", "echo output && exit /b 1"));
-        } else {
-            output = assertDoesNotThrow(() -> ProcessRunner.runWithOutput("sh", "-c", "echo output; exit 1"));
-        }
+        String[] command = shellCommand("echo output; exit 1");
+        String output = assertDoesNotThrow(() -> ProcessRunner.runWithOutput(command));
 
         assertNotNull(output, "Output should not be null");
         assertTrue(output.contains("output"), "Output should contain 'output'");
     }
 
     @Test
     void runWithOutput_capturesStderrViaMergedStream() {
-        String output;
-        if (isWindows()) {
-            output = ProcessRunner.runWithOutput("cmd.exe", "/c", "echo stdout && echo stderr 1>&2");
-        } else {
-            output = ProcessRunner.runWithOutput("sh", "-c", "echo stdout && echo stderr 1>&2");
-        }
+        String output = ProcessRunner.runWithOutput(shellCommand("echo stdout && echo stderr 1>&2"));
 
         assertNotNull(output, "Output should not be null");
         assertFalse(output.isEmpty(), "Output should not be empty");