Fix frame deduplication and chronological ordering in time series endpoint

- Fix scraping to wait for display label to change after step forward, preventing duplicate minutesAgo values within same folder
- Add hashset-based deduplication by AbsoluteObservationTime across cache folders
- Filter frames that are too close together (< 4 minutes apart)
- Preserve original folder structure while pruning filtered frames
- Sort folders by earliest frame time to maintain chronological order
- Add validation to detect folder overlaps that could cause out-of-order frames

Models/CacheFolder.cs

@@ -0,0 +1,33 @@
+namespace BomLocalService.Models;
+
+/// <summary>
+/// Information about a cache folder containing cached data for a location.
+/// Each cache folder represents one capture session and can contain multiple data types.
+/// </summary>
+public class CacheFolder
+{
+    /// <summary>
+    /// The folder name (e.g., "Pomona_QLD_20251207_000906").
+    /// </summary>
+    public string FolderName { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// The UTC timestamp when this cache folder was created (extracted from folder name).
+    /// </summary>
+    public DateTime CacheTimestamp { get; set; }
+    
+    /// <summary>
+    /// The observation time from the metadata (when the weather data was captured by BOM).
+    /// </summary>
+    public DateTime ObservationTime { get; set; }
+    
+    /// <summary>
+    /// List of data types available in this cache folder.
+    /// </summary>
+    public List<CachedDataType> AvailableDataTypes { get; set; } = new();
+    
+    /// <summary>
+    /// Whether this cache folder is complete and ready to use.
+    /// </summary>
+    public bool IsComplete { get; set; }
+}