Standardize API error responses with RFC 7807 ProblemDetails

- Add NotFoundProblem() helper to base controller for consistent 404 responses
- Add global ProducesResponseType for 500 errors on base controller
- Update GetByKeyIssueController to return IActionResult with proper NotFound
- Update DeleteAuditController to return ProblemDetails on NotFound

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: rickbutterfield

src/Umbraco.Community.ContentAudit/Api/Audit/DeleteAuditController.cs

@@ -21,11 +21,11 @@ public DeleteAuditController(IDataService dataService) : base(dataService) { }
         /// <param name="id">Audit unique identifier.</param>
         [HttpDelete("{id:guid}")]
         [ProducesResponseType(StatusCodes.Status200OK)]
-        [ProducesResponseType(StatusCodes.Status404NotFound)]
-        public async Task<ActionResult> Delete(Guid id)
+        [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status404NotFound)]
+        public async Task<IActionResult> Delete(Guid id)
         {
             var result = await DataService.DeleteAudit(id);
-            return result ? Ok() : NotFound();
+            return result ? Ok() : NotFoundProblem("Audit", id);
         }
     }
 }

src/Umbraco.Community.ContentAudit/Api/ContentAuditManagementApiControllerBase.cs

@@ -1,4 +1,5 @@
-using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
 using Umbraco.Cms.Api.Common.Attributes;
 using Umbraco.Community.ContentAudit.Api.Audit;
 
@@ -12,15 +13,34 @@ namespace Umbraco.Community.ContentAudit.Api
     /// - Maps all derived controllers to the "content-audit" API namespace
     /// - Applies [ApiController] attribute for automatic model validation and binding
     /// - Inherits from <see cref="Controller"/> to provide standard MVC controller functionality
-    /// 
+    ///
     /// All Content Audit API controllers should derive from this base class either directly
     /// or through intermediate base classes like <see cref="AuditControllerBase"/>.
-    /// 
+    ///
     /// The [MapToApi] attribute ensures all endpoints are properly routed under the
     /// "/umbraco/content-audit/management/api/v1/" path prefix.
     /// </remarks>
     [ApiController]
     [MapToApi("content-audit")]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status500InternalServerError)]
     public class ContentAuditManagementApiControllerBase : Controller
-    { }
+    {
+        /// <summary>
+        /// Creates a NotFound response with RFC 7807 ProblemDetails.
+        /// </summary>
+        /// <param name="resourceType">The type of resource that was not found.</param>
+        /// <param name="id">The identifier that was searched for.</param>
+        protected NotFoundObjectResult NotFoundProblem(string resourceType, Guid id)
+        {
+            var problemDetails = new ProblemDetails
+            {
+                Status = StatusCodes.Status404NotFound,
+                Title = $"{resourceType} not found",
+                Detail = $"No {resourceType.ToLowerInvariant()} with id '{id}' was found.",
+                Type = "https://tools.ietf.org/html/rfc7807",
+                Instance = HttpContext?.Request.Path
+            };
+            return NotFound(problemDetails);
+        }
+    }
 }

src/Umbraco.Community.ContentAudit/Api/Issues/GetByKeyIssueController.cs

@@ -1,3 +1,4 @@
+using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
 using Umbraco.Community.ContentAudit.Interfaces;
 using Umbraco.Community.ContentAudit.Models.Dtos;
@@ -20,8 +21,12 @@ public GetByKeyIssueController(IDataService dataService) : base(dataService) { }
         /// </summary>
         /// <param name="id">Issue unique identifier.</param>
         [HttpGet("{id:guid}")]
-        [ProducesResponseType(typeof(IssueDto), 200)]
-        public async Task<IssueDto?> GetIssue(Guid id)
-            => await DataService.GetIssue(id);
+        [ProducesResponseType(typeof(IssueDto), StatusCodes.Status200OK)]
+        [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status404NotFound)]
+        public async Task<IActionResult> GetIssue(Guid id)
+        {
+            var issue = await DataService.GetIssue(id);
+            return issue != null ? Ok(issue) : NotFoundProblem("Issue", id);
+        }
     }
 }