Add REST controller with RFC 9457 error handling

EventController for POST /events, GlobalExceptionHandler mapping
validation and business exceptions to problem+json responses.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/main/java/de/fete/adapter/in/web/EventController.java

@@ -0,0 +1,46 @@
+package de.fete.adapter.in.web;
+
+import de.fete.adapter.in.web.api.EventsApi;
+import de.fete.adapter.in.web.model.CreateEventRequest;
+import de.fete.adapter.in.web.model.CreateEventResponse;
+import de.fete.domain.model.CreateEventCommand;
+import de.fete.domain.model.Event;
+import de.fete.domain.port.in.CreateEventUseCase;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.RestController;
+
+/** REST controller for event operations. */
+@RestController
+public class EventController implements EventsApi {
+
+  private final CreateEventUseCase createEventUseCase;
+
+  /** Creates a new controller with the given use case. */
+  public EventController(CreateEventUseCase createEventUseCase) {
+    this.createEventUseCase = createEventUseCase;
+  }
+
+  @Override
+  public ResponseEntity<CreateEventResponse> createEvent(
+      CreateEventRequest request) {
+    var command = new CreateEventCommand(
+        request.getTitle(),
+        request.getDescription(),
+        request.getDateTime(),
+        request.getLocation(),
+        request.getExpiryDate()
+    );
+
+    Event event = createEventUseCase.createEvent(command);
+
+    var response = new CreateEventResponse();
+    response.setEventToken(event.getEventToken());
+    response.setOrganizerToken(event.getOrganizerToken());
+    response.setTitle(event.getTitle());
+    response.setDateTime(event.getDateTime());
+    response.setExpiryDate(event.getExpiryDate());
+
+    return ResponseEntity.status(HttpStatus.CREATED).body(response);
+  }
+}

backend/src/main/java/de/fete/adapter/in/web/GlobalExceptionHandler.java

@@ -0,0 +1,71 @@
+package de.fete.adapter.in.web;
+
+import de.fete.application.service.ExpiryDateInPastException;
+import java.net.URI;
+import java.util.List;
+import java.util.Map;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.HttpStatusCode;
+import org.springframework.http.MediaType;
+import org.springframework.http.ProblemDetail;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.MethodArgumentNotValidException;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+import org.springframework.web.context.request.WebRequest;
+import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;
+
+/** Global exception handler producing RFC 9457 Problem Details responses. */
+@RestControllerAdvice
+public class GlobalExceptionHandler extends ResponseEntityExceptionHandler {
+
+  @Override
+  protected ResponseEntity<Object> handleMethodArgumentNotValid(
+      MethodArgumentNotValidException ex,
+      HttpHeaders headers,
+      HttpStatusCode status,
+      WebRequest request) {
+
+    ProblemDetail problemDetail = ex.getBody();
+    problemDetail.setTitle("Validation Failed");
+    problemDetail.setType(URI.create("urn:problem-type:validation-error"));
+
+    List<Map<String, String>> fieldErrors = ex.getBindingResult()
+        .getFieldErrors()
+        .stream()
+        .map(fe -> Map.of(
+            "field", fe.getField(),
+            "message", fe.getDefaultMessage() != null ? fe.getDefaultMessage() : "invalid"
+        ))
+        .toList();
+
+    problemDetail.setProperty("fieldErrors", fieldErrors);
+    return handleExceptionInternal(ex, problemDetail, headers, status, request);
+  }
+
+  /** Handles expiry date validation failures. */
+  @ExceptionHandler(ExpiryDateInPastException.class)
+  public ResponseEntity<ProblemDetail> handleExpiryDateInPast(
+      ExpiryDateInPastException ex) {
+    ProblemDetail problemDetail = ProblemDetail.forStatusAndDetail(
+        HttpStatus.BAD_REQUEST, ex.getMessage());
+    problemDetail.setTitle("Invalid Expiry Date");
+    problemDetail.setType(URI.create("urn:problem-type:expiry-date-in-past"));
+    return ResponseEntity.badRequest()
+        .contentType(MediaType.APPLICATION_PROBLEM_JSON)
+        .body(problemDetail);
+  }
+
+  /** Catches all unhandled exceptions. */
+  @ExceptionHandler(Exception.class)
+  public ResponseEntity<ProblemDetail> handleAll(Exception ex) {
+    ProblemDetail problemDetail = ProblemDetail.forStatusAndDetail(
+        HttpStatus.INTERNAL_SERVER_ERROR,
+        "An unexpected error occurred.");
+    problemDetail.setTitle("Internal Server Error");
+    return ResponseEntity.internalServerError()
+        .contentType(MediaType.APPLICATION_PROBLEM_JSON)
+        .body(problemDetail);
+  }
+}