Add Hurl smoke tests for examples

[lovasoa]

Summary

Adds Docker Compose coverage and a shared Hurl smoke test for the examples.

• Adds docker-compose.yml files for examples that were missing one.
• Adds one root test.hurl smoke test and symlinks it into each example so the runner can simply discover and run example-local tests.
• Adds scripts/test-examples-hurl.sh, which starts each example compose stack, runs its test.hurl, and tears the stack down.
• Adds a focused GitHub Actions workflow for the example Hurl tests.
• Removes unnecessary database host-port publishing and avoids building SQLPage from source in example smoke paths where the public image is enough.

Validation

• hurlfmt --check test.hurl
• bash -n scripts/test-examples-hurl.sh
• docker compose -f ... config --quiet for all example compose files
• git diff --check
• Local Hurl runs passed for representative examples including plots tables and forms, SQLPage developer user interface, corporate-conundrum, and the suite up to the MSSQL example.

Local full-suite validation stopped at the MSSQL example because SQL Server 2022 does not run cleanly under macOS arm64/QEMU in this environment. The draft PR is intended to let GitHub Actions validate that case on Ubuntu amd64.