feat(nlp2dsl): constrain live conversation fields

[tom-sapletta-com]

Summary

• publish ConversationFields v1 as GBNF, Protobuf, JSON Schema, fixtures, and boundary manifest
• require structured output and strict whole-response validation in LiveLLMProvider
• reject response fields outside the requested missing set while preserving the existing plain llmContext mapping
• normalize the OpenRouter GLM 5.2 model ID and send App identity through X-Title

Verification

• python -m pytest -q --no-cov (1679 passed, 17 skipped)
• changed-file Ruff check/format pass
• wheel inspection confirms both TestQL contract bundles and no bytecode cache

Stack

This PR targets the nlp2env contract branch and should merge after #1. Once #1 is on main, this PR can be retargeted/rebased without mixing the two runtime boundaries.