docs: surface premise in prompt-construction integrations

[rlippmann]

Summary

Surface premise more clearly in existing prompt-construction runtime and reference integrations.

This PR does not add new examples or change runtime mechanics. It updates docs and focused tests so existing integrations visibly show premise as authoritative context alongside policy.

Updated surfaces include:

• LiteLLM prompt construction
• Open WebUI pipe reference integration
• Next.js starter apps

Why

The generic writing-assistant example now distinguishes premise from policy directly.

These runtime/reference prompt-construction surfaces already supported premise, but the docs and tests emphasized policy more clearly than premise. This made premise less visible even though it was already part of the constructed request/state contract.

This PR makes the existing behavior explicit:

• Premise = authoritative factual/request context
• Policy = explicit behavioral constraint

Example metadata

• Enforcement point: prompt construction / request construction
• Domain: writing assistant / request construction
• Technology/runtime: LiteLLM, Open WebUI pipe, Next.js starter apps
• Example type: reference integration / starter app / documentation cleanup
• Does this use directive drafter? should normally be no: no for the LiteLLM/Open WebUI/basic Next.js paths; existing with-drafter starter remains unchanged
• Does this derive state from model output? must be no for primary examples: no

Checklist

• Repository scaffolding / governance change
• One primary enforcement point
• Explicit authoritative state
• No model-derived state mutation
• Adversarial stub or equivalent test
• Observable runtime behavior change
• Domain vocabulary is natural
• Framework is secondary to the enforcement point
• Docs updated
• Tests/smoke checks added where practical

Notes

Validation performed:

• uv run --no-sync pytest python/tests/test_litellm_basic.py python/tests/test_openwebui_pipe.py
• ./scripts/validate_python.sh
• node --test typescript/starter_apps/nextjs/basic/tests/smoke.test.mjs
• node --test typescript/starter_apps/nextjs/with_drafter/tests/smoke.test.mjs
• ./scripts/validate_typescript_fast.sh
• npx --yes markdownlint-cli2 python/examples/prompt_construction/litellm/README.md python/reference_integrations/openwebui_pipe/README.md typescript/starter_apps/nextjs/basic/README.md typescript/starter_apps/nextjs/with_drafter/README.md

All validation passed.