feat(data): rename *.Services projects, lift TrackEntity onto BlazorBlocks data layer, regenerate initial Postgres migration

DeepDrftWeb.Services → DeepDrftData; DeepDrftContent.Services → DeepDrftContent.Data.
TrackEntity:BaseEntity, TrackRepository:Repository<>, TrackManager:Manager<>+ITrackService.
Drops DeepDrftModels PagingParameters/PagedResult in favour of Models.Common.* from BlazorBlocks.
InitialCreate migration captures full schema including is_deleted index.

DeepDrftContent.Data/FileDatabase/Utils/StructuralMap.cs

@@ -0,0 +1,125 @@
+using System.Collections;
+using System.Text.Json;
+
+namespace DeepDrftContent.Data.FileDatabase.Utils;
+
+/// <summary>
+/// A map implementation that uses structural equality for keys by serializing them to JSON.
+/// This provides the same behavior as the TypeScript StructuralMap.
+/// Optimized with caching to avoid repeated serialization.
+/// </summary>
+/// <typeparam name="TKey">The key type</typeparam>
+/// <typeparam name="TValue">The value type</typeparam>
+public class StructuralMap<TKey, TValue> : IEnumerable<KeyValuePair<TKey, TValue>> where TKey : notnull
+{
+    private readonly Dictionary<string, KeyValuePair<TKey, TValue>> _innerMap = new();
+    private readonly Dictionary<TKey, string> _keyStringCache = new();
+
+    /// <summary>
+    /// Converts a key to its string representation for structural comparison
+    /// Uses caching to avoid expensive serialization on repeated lookups
+    /// </summary>
+    private string GetKeyString(TKey key)
+    {
+        if (key == null) return "null";
+        
+        // For reference types, use cache to avoid repeated serialization
+        if (!typeof(TKey).IsValueType && _keyStringCache.TryGetValue(key, out var cached))
+        {
+            return cached;
+        }
+
+        var keyString = key switch
+        {
+            string s => s,
+            int or long or float or double or decimal => key.ToString()!,
+            _ => JsonSerializer.Serialize(key)
+        };
+
+        // Cache for reference types only (value types are cheap to convert)
+        if (!typeof(TKey).IsValueType)
+        {
+            _keyStringCache[key] = keyString;
+        }
+
+        return keyString;
+    }
+
+    /// <summary>
+    /// Sets a key-value pair in the map
+    /// </summary>
+    public StructuralMap<TKey, TValue> Set(TKey key, TValue value)
+    {
+        var keyString = GetKeyString(key);
+        _innerMap[keyString] = new KeyValuePair<TKey, TValue>(key, value);
+        return this;
+    }
+
+    /// <summary>
+    /// Gets a value by key, or default if not found
+    /// </summary>
+    public TValue? Get(TKey key)
+    {
+        var keyString = GetKeyString(key);
+        return _innerMap.TryGetValue(keyString, out var pair) ? pair.Value : default;
+    }
+
+    /// <summary>
+    /// Checks if the map contains the specified key
+    /// </summary>
+    public bool Has(TKey key)
+    {
+        var keyString = GetKeyString(key);
+        return _innerMap.ContainsKey(keyString);
+    }
+
+    /// <summary>
+    /// Removes a key-value pair from the map
+    /// </summary>
+    public bool Delete(TKey key)
+    {
+        var keyString = GetKeyString(key);
+        return _innerMap.Remove(keyString);
+    }
+
+    /// <summary>
+    /// Clears all entries from the map
+    /// </summary>
+    public void Clear() => _innerMap.Clear();
+
+    /// <summary>
+    /// Gets the number of entries in the map
+    /// </summary>
+    public int Size => _innerMap.Count;
+
+    /// <summary>
+    /// Enumerates all key-value pairs
+    /// </summary>
+    public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
+    {
+        return _innerMap.Values.GetEnumerator();
+    }
+
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+
+    /// <summary>
+    /// Gets all keys in the map
+    /// </summary>
+    public IEnumerable<TKey> Keys => _innerMap.Values.Select(pair => pair.Key);
+
+    /// <summary>
+    /// Gets all values in the map
+    /// </summary>
+    public IEnumerable<TValue> Values => _innerMap.Values.Select(pair => pair.Value);
+
+    /// <summary>
+    /// Executes a callback for each key-value pair
+    /// </summary>
+    public void ForEach(Action<TValue, TKey, StructuralMap<TKey, TValue>> callback)
+    {
+        foreach (var (key, value) in this)
+        {
+            callback(value, key, this);
+        }
+    }
+}