fix: sync latest conformance API helpers and use 0.7 helpers in examples

[rlippmann]

Summary

• Re-synced portable Python fixtures into TS (full conformance + preprocessor sync), which updated the API contract fixture and fixture README wording.
• Added minimal TS public API parity for newly fixture-required helper exports and policy constants:
  • is_update, is_clarify, is_passthrough
  • get_clarify_prompt, get_decision_state
  • POLICY_USE, POLICY_PROHIBIT
• Updated API parity mapping test to include those new fixture-required exports.
• Updated examples/demos (and quick-start README snippet) to prefer 0.7 helper functions/constants where it improved readability, without behavior changes.
• Updated Node and Next.js integration handlers to use is_clarify, DECISION_CLARIFY, and POLICY_USE where it improved readability without control-flow changes.
• Updated CI fixture pin (PY_FIXTURE_REF) to the synced Python fixture snapshot commit used by this branch.

Why

Python fixture updates added helper/constant API contract requirements. TS needed minimal export-layer parity to satisfy that contract. CI also needed its pinned Python fixture ref advanced so fixture drift checks compare against the same snapshot synced into this branch.

Scope checklist

• Diff is minimal and scoped to the requested behavior
• Python/spec parity is preserved (or mismatch is explicitly documented)
• Fixture semantics are respected (exact string vs non-empty null rule)
• No unrelated refactors
• Relevant validation was run (npm test for behavior changes, or docs-only/no-runtime-change)

Notes

Validation details:

• npm test: passed
• If not run, why: n/a