feat: add uptime command and moved target dir to .gitignore

Author: yuvii-b

.gitignore

@@ -0,0 +1 @@
+target/

src/main/java/com/mycmd/App.java

@@ -78,5 +78,6 @@ private static void registerCommands(Map<String, Command> commands) {
         commands.put("date", new DateCommand());
         commands.put("history", new HistoryCommand());
         commands.put("pwd", new PwdCommand());
+        commands.put("uptime", new UptimeCommand());
     }
 }

src/main/java/com/mycmd/ShellContext.java

@@ -7,11 +7,13 @@
 public class ShellContext {
     private File currentDir;
     private List<String> commandHistory;
+    private final long startTime;
     private static final int MAX_HISTORY = 10;
 
     public ShellContext() {
         this.currentDir = new File(System.getProperty("user.dir"));
         this.commandHistory = new ArrayList<>();
+        this.startTime = System.currentTimeMillis();
     }
 
     public File getCurrentDir() {
@@ -22,6 +24,10 @@ public void setCurrentDir(File dir) {
         this.currentDir = dir;
     }
 
+    public long getStartTime() {
+        return startTime;
+    }
+
     public List<String> getCommandHistory() {
         return commandHistory;
     }

src/main/java/com/mycmd/commands/UptimeCommand.java

@@ -0,0 +1,45 @@
+package com.mycmd.commands;
+
+import com.mycmd.Command;
+import com.mycmd.ShellContext;
+
+/**
+ * Displays how long the shell has been running since startup.
+ * 
+ * This command shows the uptime of the MyCMD shell session, displaying
+ * the time elapsed since the shell was started. The uptime is calculated
+ * from the shell start time stored in the ShellContext.
+ * 
+ * Usage:
+ * - uptime : Display shell uptime in hours, minutes, and seconds
+ * 
+ * The output format shows the uptime as "Up since Xh Ym Zs" where:
+ * - X is hours
+ * - Y is minutes  
+ * - Z is seconds
+ * 
+ * This is useful for monitoring how long a shell session has been active.
+ */
+public class UptimeCommand implements Command {
+    @Override
+    public void execute(String[] args, ShellContext context) {
+        long uptimeMillis = System.currentTimeMillis() - context.getStartTime();
+        
+        long totalSeconds = uptimeMillis / 1000;
+        long hours = totalSeconds / 3600;
+        long minutes = (totalSeconds % 3600) / 60;
+        long seconds = totalSeconds % 60;
+        
+        System.out.printf("Up since %dh %dm %ds%n", hours, minutes, seconds);
+    }
+
+    @Override
+    public String description() {
+        return "Display how long the shell has been running since startup.";
+    }
+
+    @Override
+    public String usage() {
+        return "uptime";
+    }
+}