refactor: modularize Beam into new projects and interfaces

- Introduced modularity by splitting Beam into new projects: Beam.Abstractions, Beam.Models, and Beam.Downloaders.
- Refactored existing classes into appropriate namespaces and projects.
- Replaced specific implementations with abstractions (e.g., SourceLinkBuilder to LinkBuilder, State to IState, etc.).
- Updated interfaces: added ITemplate, IArticleData, IDownloadReport, and others for improved extensibility.
- Removed deprecated classes like SourceLinkBuilder and StateChangerFactory.
- Enhanced link handling in downloaders by refactoring to use `string` over `SourceLink`.
- Consolidated shared logic under Beam.Abstractions.

Beam.Data/ResourceDictionary.cs

@@ -0,0 +1,19 @@
+using System.Text.Json.Serialization;
+using aeqw89.DataKeys;
+using Beam.Abstractions;
+using Beam.Models;
+
+namespace Beam.Data {
+    public class ResourceDictionary : IKeyed<ResourceDictionary>, IResourceDictionary {
+        public required DataKey<ResourceDictionary> Key { get; set; }
+
+        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+        public string? FriendlyName { get; set; }
+
+        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
+        public Dictionary<string, DataKey<WebResource>> Resources { get; set; } = [];
+
+        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
+        public Dictionary<DataKey<WebResource>, ImmutableState> InitialStates { get; set; } = [];
+    }
+}