feat: add domain exceptions and global error handler

src/main/java/com/slotline/common/AvailabilityViolationException.java

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+package com.slotline.common;
+
+public class AvailabilityViolationException extends RuntimeException {
+
+    public AvailabilityViolationException(String message) {
+        super(message);
+    }
+}

src/main/java/com/slotline/common/ForbiddenOperationException.java

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+package com.slotline.common;
+
+public class ForbiddenOperationException extends RuntimeException {
+
+    public ForbiddenOperationException(String message) {
+        super(message);
+    }
+}

src/main/java/com/slotline/common/GlobalExceptionHandler.java

@@ -0,0 +1,86 @@
+package com.slotline.common;
+
+import com.slotline.recurrence.RecurrenceException;
+import jakarta.servlet.http.HttpServletRequest;
+import org.springframework.dao.ConcurrencyFailureException;
+import org.springframework.dao.DataIntegrityViolationException;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ProblemDetail;
+import org.springframework.http.ResponseEntity;
+import org.springframework.http.converter.HttpMessageNotReadableException;
+import org.springframework.web.bind.MethodArgumentNotValidException;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+
+import java.util.List;
+
+@RestControllerAdvice
+public class GlobalExceptionHandler {
+
+    @ExceptionHandler(NotFoundException.class)
+    public ResponseEntity<ProblemDetail> handleNotFound(NotFoundException exception, HttpServletRequest request) {
+        return problem(HttpStatus.NOT_FOUND, exception.getMessage(), request);
+    }
+
+    @ExceptionHandler(InvalidCredentialsException.class)
+    public ResponseEntity<ProblemDetail> handleInvalidCredentials(InvalidCredentialsException exception,
+                                                                  HttpServletRequest request) {
+        return problem(HttpStatus.UNAUTHORIZED, exception.getMessage(), request);
+    }
+
+    @ExceptionHandler(ForbiddenOperationException.class)
+    public ResponseEntity<ProblemDetail> handleForbidden(ForbiddenOperationException exception,
+                                                         HttpServletRequest request) {
+        return problem(HttpStatus.FORBIDDEN, exception.getMessage(), request);
+    }
+
+    @ExceptionHandler({InvalidReservationException.class, RecurrenceException.class})
+    public ResponseEntity<ProblemDetail> handleInvalidReservation(RuntimeException exception,
+                                                                  HttpServletRequest request) {
+        return problem(HttpStatus.BAD_REQUEST, exception.getMessage(), request);
+    }
+
+    @ExceptionHandler(AvailabilityViolationException.class)
+    public ResponseEntity<ProblemDetail> handleAvailability(AvailabilityViolationException exception,
+                                                            HttpServletRequest request) {
+        return problem(HttpStatus.UNPROCESSABLE_ENTITY, exception.getMessage(), request);
+    }
+
+    @ExceptionHandler({SlotConflictException.class, UsernameTakenException.class, SlugTakenException.class})
+    public ResponseEntity<ProblemDetail> handleConflict(RuntimeException exception, HttpServletRequest request) {
+        return problem(HttpStatus.CONFLICT, exception.getMessage(), request);
+    }
+
+    @ExceptionHandler({ConcurrencyFailureException.class, DataIntegrityViolationException.class})
+    public ResponseEntity<ProblemDetail> handleConcurrentBooking(RuntimeException exception,
+                                                                 HttpServletRequest request) {
+        return problem(HttpStatus.CONFLICT, "The slot was booked by a concurrent request", request);
+    }
+
+    @ExceptionHandler(HttpMessageNotReadableException.class)
+    public ResponseEntity<ProblemDetail> handleUnreadable(HttpMessageNotReadableException exception,
+                                                          HttpServletRequest request) {
+        return problem(HttpStatus.BAD_REQUEST, "Malformed request body", request);
+    }
+
+    @ExceptionHandler(MethodArgumentNotValidException.class)
+    public ResponseEntity<ProblemDetail> handleValidation(MethodArgumentNotValidException exception,
+                                                          HttpServletRequest request) {
+        List<FieldViolation> violations = exception.getBindingResult().getFieldErrors().stream()
+                .map(error -> new FieldViolation(error.getField(), error.getDefaultMessage()))
+                .toList();
+        ResponseEntity<ProblemDetail> response = problem(HttpStatus.BAD_REQUEST, "Request validation failed", request);
+        response.getBody().setProperty("violations", violations);
+        return response;
+    }
+
+    private ResponseEntity<ProblemDetail> problem(HttpStatus status, String detail, HttpServletRequest request) {
+        ProblemDetail body = ProblemDetail.forStatusAndDetail(status, detail);
+        body.setTitle(status.getReasonPhrase());
+        body.setProperty("path", request.getRequestURI());
+        return ResponseEntity.status(status).body(body);
+    }
+
+    private record FieldViolation(String field, String message) {
+    }
+}

src/main/java/com/slotline/common/InvalidCredentialsException.java

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+package com.slotline.common;
+
+public class InvalidCredentialsException extends RuntimeException {
+
+    public InvalidCredentialsException() {
+        super("Invalid username or password");
+    }
+}

src/main/java/com/slotline/common/InvalidReservationException.java

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+package com.slotline.common;
+
+public class InvalidReservationException extends RuntimeException {
+
+    public InvalidReservationException(String message) {
+        super(message);
+    }
+}

src/main/java/com/slotline/common/NotFoundException.java

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+package com.slotline.common;
+
+public class NotFoundException extends RuntimeException {
+
+    public NotFoundException(String message) {
+        super(message);
+    }
+}

src/main/java/com/slotline/common/SlotConflictException.java

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+package com.slotline.common;
+
+public class SlotConflictException extends RuntimeException {
+
+    public SlotConflictException(String message) {
+        super(message);
+    }
+}

src/main/java/com/slotline/common/SlugTakenException.java

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+package com.slotline.common;
+
+public class SlugTakenException extends RuntimeException {
+
+    public SlugTakenException(String slug) {
+        super("Organization slug '" + slug + "' is already taken");
+    }
+}

src/main/java/com/slotline/common/UsernameTakenException.java

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+package com.slotline.common;
+
+public class UsernameTakenException extends RuntimeException {
+
+    public UsernameTakenException(String username) {
+        super("Username '" + username + "' is already taken");
+    }
+}