feat: add DecisionPort semantic judgement capability

[colmugx]

Summary

• add a provider-neutral DecisionPort::evaluate(DecisionRequest) seam for structured semantic judgement without routing through ModelPort
• model typed Boolean / Choice / Score questions and probabilistic answers, with request/result invariant validation
• compose DecisionPort as an optional singleton capability (Capability::Decision, CompositionView::decision()), with MultipleDecisions fail-fast cardinality
• add ScriptedDecisionPort testkit support and focused conformance/composition tests
• keep DecisionPort out of Kernel/Puppet execution: it supplies judgement only; consuming extensions retain policy and authority

Compatibility

ExtensionManifest gains a decisions field. Direct record literals must add decisions: []; callers using ExtensionManifest::empty(...) remain source-compatible.

Validation

Verified from an exact main@e4fa4b07fe2b581dbee952d831009c322a906909 source snapshot using the official MoonBit toolchain (moon 0.1.20260915, moonc v0.10.13+cbb11c36f).

• baseline native suite: 500/500
• focused DecisionPort tests: 5/5
• full native suite after change: 505/505
• clean rebuild after moon clean: 505/505
• moon fmt --check: pass
• moon check --target native --output-json: 0 errors
• moon info: pass, generated .mbti checked in and clean

The formal branch is a single commit directly on main; temporary environment/bootstrap files are not part of the PR.