feat(backend): add sentry-spring-boot-starter-jakarta for GlitchTip error reporting

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

docker-compose.yml

@@ -147,6 +147,7 @@ services:
       SPRING_MAIL_PROPERTIES_MAIL_SMTP_STARTTLS_ENABLE: ${MAIL_STARTTLS_ENABLE:-false}
       APP_OCR_BASE_URL: http://ocr-service:8000
       APP_OCR_TRAINING_TOKEN: "${OCR_TRAINING_TOKEN:-}"
+      SENTRY_DSN: ${SENTRY_DSN:-}
       # Observability: send traces to Tempo inside archiv-net (OTLP gRPC port 4317)
       # Tempo is defined in docker-compose.observability.yml (future issue).
       # OTLP failures are non-fatal — backend starts cleanly without the observability stack.