fix: InvalidClientTokenId panic + VT defaults + Dockerfile config + hardcore tests (58/61)

- Add InvalidClientTokenId, ValidationError to SqsErrors (was causing panic: WriteHeader code 0)
- Extract applyEnvironmentDefaults() with defer in LoadYamlConfig (VT=30 even without config file)
- Dockerfile: copy goaws.yaml to /conf/, pass --config flag
- Fix SendMessageBatch form parsing for AWS Query Protocol
- Add hardcore_test.sh (61 tests, 14 groups)
- Remove temp debug logs from delete_message.go

shared-sqs/Dockerfile

@@ -11,7 +11,8 @@ RUN CGO_ENABLED=0 go build -o shared-sqs app/cmd/goaws.go
 FROM alpine:3.19
 RUN apk --no-cache add ca-certificates
 COPY --from=builder /build/shared-sqs /usr/local/bin/shared-sqs
+COPY --from=builder /build/app/conf/goaws.yaml /conf/goaws.yaml
 EXPOSE 4100
 HEALTHCHECK --interval=10s --timeout=5s --retries=3 \
   CMD wget -q -O - http://localhost:4100/health || exit 1
-ENTRYPOINT ["shared-sqs"]
+ENTRYPOINT ["shared-sqs", "--config", "/conf/goaws.yaml"]