Add problem-details: global exception handling with RFC 9457

Companion code for "Global Exception Handling with ProblemDetail (RFC 9457)
in Spring Boot 4". Thirteen failures under five handling setups (Boot
defaults, the Boot flag, a ResponseEntityExceptionHandler advice, advice
plus an ErrorController, a catch-all ordered first), validation errors,
i18n, content negotiation, Security's 401/403, silent 500s and decoding
on the client. 16 tests pin the behaviour.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01C3TETMrqVUWeFkNtz3Jbo3

problem-details/scripts/run.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+# Start the application with the given profiles (comma-separated, may be empty) and wait until it
+# answers. Any instance started by a previous run is stopped first, by PID file - never by
+# pattern-matching the process list, which can match (and kill) the calling shell.
+#   ./scripts/run.sh advice
+#   ./scripts/run.sh ""            # Spring Boot defaults
+set -euo pipefail
+source "$(dirname "$0")/env.sh"
+"$MODULE_DIR/scripts/stop.sh"
+PROFILES="${1:-}"
+[ -f "$JAR" ] || (cd "$MODULE_DIR" && mvn -q -DskipTests package)
+nohup java -jar "$JAR" --server.port="$PORT" ${PROFILES:+--spring.profiles.active=$PROFILES} ${EXTRA_ARGS:-} \
+  > "$LOG" 2>&1 < /dev/null &
+echo $! > "$PIDFILE"
+for _ in $(seq 1 60); do
+  if curl -s -o /dev/null "$BASE/orders/1"; then exit 0; fi
+  if ! kill -0 "$(cat "$PIDFILE")" 2>/dev/null; then echo "application exited - see $LOG" >&2; exit 1; fi
+  sleep 0.5
+done
+echo "application did not start within 30s - see $LOG" >&2; exit 1