Implement automatic deletion of old screenshots

This change introduces a limit to the number of screenshots stored by the ScreenCaptureService. When a new screenshot is taken, I now check the number of existing screenshots in the app's dedicated screenshot directory (`Android/data/com.google.ai.sample/files/Pictures/Screenshots/`).

If saving a new screenshot would cause the total to exceed 100, the oldest screenshot(s) are deleted to maintain a maximum of 100. Screenshots are identified by the naming pattern "screenshot_yyyyMMdd_HHmmss.png", allowing for reliable sorting to find the oldest ones.

Logging has been added to record the deletion of old screenshots or any failures in the deletion process.

Manual testing is required to confirm this functionality by generating more than 100 screenshots and observing the file system and logs.

Author: google-labs-jules[bot]

app/src/main/kotlin/com/google/ai/sample/ScreenCaptureService.kt

@@ -332,6 +332,33 @@ private fun takeScreenshot() {
                 picturesDir.mkdirs()
             }
 
+            // List existing screenshot files
+            val screenshotFiles = picturesDir.listFiles { _, name ->
+                name.startsWith("screenshot_") && name.endsWith(".png")
+            }?.toMutableList() ?: mutableListOf()
+
+            // Sort files by name (timestamp) to find the oldest
+            screenshotFiles.sortBy { it.name }
+
+            // If count is 100 or more, delete oldest ones until count is 99
+            // This makes space for the new screenshot, keeping the total at a max of 100
+            val maxScreenshots = 100
+            var screenshotsToDelete = screenshotFiles.size - (maxScreenshots -1) // Number of files to delete to make space for the new one
+
+            if (screenshotsToDelete > 0) {
+                Log.i(TAG, "Max screenshots reached. Current count: ${screenshotFiles.size}. Attempting to delete $screenshotsToDelete oldest screenshot(s).")
+                for (i in 0 until screenshotsToDelete) {
+                    if (i < screenshotFiles.size) {
+                        val oldestFile = screenshotFiles[i]
+                        if (oldestFile.delete()) {
+                            Log.i(TAG, "Deleted oldest screenshot: ${oldestFile.absolutePath}")
+                        } else {
+                            Log.e(TAG, "Failed to delete oldest screenshot: ${oldestFile.absolutePath}")
+                        }
+                    }
+                }
+            }
+
             val timestamp = SimpleDateFormat("yyyyMMdd_HHmmss", Locale.getDefault()).format(Date())
             val file = File(picturesDir, "screenshot_$timestamp.png")