Cover workflow definition contracts

[rmcdaniel]

Summary

• cover workflow definition command discovery, aliases, portable parameter contracts, and invalid definitions
• prove duplicate durable query, update, and signal names fail before worker registration becomes ambiguous
• cover inherited and trait-backed definition fingerprints and the final nullable query-metadata fallback
• advance the accepted coverage floor to the 85.53% result already proven on main

Verification

• WorkflowDefinitionContractTest: 10 tests, 63 assertions
• modified query-contract case: 1 test, 2 assertions
• ECS: clean
• PHPStan: clean
• coverage ratchet self-test: passed
• public-boundary scan: passed

Progresses #426.