docs(docstrings): add docstrings to public method interfaces (#25)

- Resolves #18

Reviewed-on: #25

src/main/java/com/ddf/vodsystem/dto/CommandOutput.java

@@ -10,6 +10,11 @@ public class CommandOutput {
     private List<String> output = new ArrayList<>();
     private int exitCode;
 
+    /**
+     * Appends a line to the captured command output.
+     *
+     * @param line the output line to append
+     */
     public void addLine(String line) {
         output.add(line);
     }

src/main/java/com/ddf/vodsystem/dto/ProgressTracker.java

@@ -4,14 +4,30 @@ public class ProgressTracker {
     private float progress = 0.0f;
     private boolean isComplete = false;
 
+    /**
+     * Returns the current progress.
+     *
+     * @return the progress as a fraction in {@code [0, 1]}
+     */
     public synchronized float getProgress() {
         return progress;
     }
 
+    /**
+     * Returns whether the tracked task has been marked complete.
+     *
+     * @return {@code true} if complete
+     */
     public synchronized boolean isComplete() {
         return isComplete;
     }
 
+    /**
+     * Updates the current progress.
+     *
+     * @param newProgress the progress as a fraction in {@code [0, 1]}
+     * @throws IllegalArgumentException if {@code newProgress} is outside {@code [0, 1]}
+     */
     public synchronized void setProgress(float newProgress) {
         if (newProgress < 0 || newProgress > 1) {
             throw new IllegalArgumentException("Progress must be between 0 and 1");
@@ -19,10 +35,16 @@ public class ProgressTracker {
         this.progress = newProgress;
     }
 
+    /**
+     * Marks the tracked task as complete.
+     */
     public synchronized void markComplete() {
         this.isComplete = true;
     }
 
+    /**
+     * Resets progress to zero and clears the complete flag.
+     */
     public synchronized void reset() {
         this.progress = 0.0f;
         this.isComplete = false;