feat(feedback): Fehler-melden-Dialog + ID-kopieren (Stammbaum/Akte/Wurf)

Rechtsklick auf eine Maus im Stammbaum öffnet ein Kontextmenü mit „ID kopieren"
(Clipboard + Toast) und „Fehler melden". Zusätzlich „Fehler melden"-Buttons in
der Rennmausakte und der Wurf-Ansicht. Der Dialog erfasst eine Beschreibung und
sendet sie samt Debug-Kontext (Ansicht, Tier-/Wurf-ID + Name, URL, Zeitstempel,
User-Agent) an POST /feedback; gespeichert in einer neuen Feedback-Tabelle.

Backend: Feedback-Entity (lose nullable GerbilId/LitterId ohne FK), Endpoints
POST/GET /feedback, EF-Migration AddFeedback. Die Tabelle wird vom Import-Ingest
NICHT geleert — Feedback überlebt Re-Ingests (Test deckt das ab).

Tests: FeedbackEndpointTests (persistiert, 400 bei leer, übersteht Ingest-Wipe);
e2e feedback.spec.ts. tsc/eslint/vitest(129)/playwright(6)/dotnet(212) grün.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

GerbilManagerWebAPI/Models/Feedback.cs

@@ -0,0 +1,44 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace GerbilManagerWebAPI.Models
+{
+    /// <summary>
+    /// FEEDBACK: a user-submitted "Fehler melden" report. Decoupled from the rest of the
+    /// model on purpose — GerbilId/LitterId are plain nullable Guid columns (NOT enforced
+    /// foreign keys), so the import re-ingest wipe (IngestResolvedService) can delete
+    /// gerbils/litters without deleting or breaking feedback rows. The captured EntityName
+    /// keeps the report human-readable even after the referenced animal is gone.
+    /// </summary>
+    public class Feedback
+    {
+        [Key]
+        public Guid Id { get; set; }
+
+        /// <summary>The user's free-text description of the problem.</summary>
+        public required string Message { get; set; }
+
+        /// <summary>Which view the report came from: stammbaum | gerbil-detail | litter-detail.</summary>
+        public required string Context { get; set; }
+
+        /// <summary>Loose reference (no FK) to the gerbil the report is about, if any.</summary>
+        public Guid? GerbilId { get; set; }
+
+        /// <summary>Loose reference (no FK) to the litter the report is about, if any.</summary>
+        public Guid? LitterId { get; set; }
+
+        /// <summary>Captured name of the referenced animal/litter (survives an ingest wipe).</summary>
+        public string? EntityName { get; set; }
+
+        /// <summary>The client URL/route the report was filed from.</summary>
+        public string? Url { get; set; }
+
+        /// <summary>Client-supplied timestamp (when the user submitted, in their browser).</summary>
+        public DateTimeOffset? ClientTimestamp { get; set; }
+
+        /// <summary>Optional browser user-agent for diagnostics.</summary>
+        public string? UserAgent { get; set; }
+
+        /// <summary>Server-side creation time.</summary>
+        public DateTimeOffset CreatedAt { get; set; }
+    }
+}