feat(backend): add knowledge base, innovation library and trends modules

Add knowledge item and innovation CRUD with search/filtering, published-only visibility for non-staff, admin publish/update, challenge dictionary, problem aggregation with trends (admin only) and canonical embedding text preparation for matchmaking.

backend/Application/Mappings/InnovationStageWire.cs

@@ -0,0 +1,29 @@
+using TarninaHub.Domain.Enums;
+
+namespace TarninaHub.Application.Mappings;
+
+public static class InnovationStageWire
+{
+    private static readonly Dictionary<string, InnovationStage> ByWire = new(StringComparer.Ordinal)
+    {
+        ["idea"] = InnovationStage.Idea,
+        ["pilot"] = InnovationStage.Pilot,
+        ["scaling"] = InnovationStage.Scaling,
+        ["service"] = InnovationStage.Service,
+    };
+
+    public static bool IsValid(string? value) =>
+        !string.IsNullOrWhiteSpace(value) && ByWire.ContainsKey(value);
+
+    public static string ToWire(this InnovationStage stage) => stage switch
+    {
+        InnovationStage.Idea => "idea",
+        InnovationStage.Pilot => "pilot",
+        InnovationStage.Scaling => "scaling",
+        InnovationStage.Service => "service",
+        _ => throw new ArgumentOutOfRangeException(nameof(stage), stage, null),
+    };
+
+    public static InnovationStage? Parse(string? value) =>
+        value is not null && ByWire.TryGetValue(value, out var stage) ? stage : null;
+}