Add string support to workflow port lookup

Create WorkflowPortLookup.java with the revised class. Assume Java 8. The current method was written in a quick pass; add the new parsing behavior and leave the method cleaner than you found it.

Current code:

import java.nio.file.Path;
import java.util.Map;
import java.util.Optional;

final class WorkflowPortLookup {
    Optional<Integer> workflowServerPortReservation(Optional<Map<String, Object>> frontMatter, Path workflowPath) {
        if (!frontMatter.isPresent()) {
            return Optional.empty();
        }
        Object value = frontMatter.get().get("server_port");
        if (value instanceof Number) {
            Number number = (Number) value;
            return Optional.of(number.intValue());
        }
        return Optional.empty();
    }
}

Required changes:

• Keep support for Number values.
• Add support for trimmed numeric String values.
• Return Optional.empty() for absent front matter, missing values, blank strings, malformed strings, and unsupported types.
• Do not throw for malformed values.
• Do not expose workflowPath in output; it is included for parity with the real method.