fix: enforce responses strict schema and resilient python runner

[fundiddad]

Summary

• enforce OpenAI Responses strict function schema by requiring all object properties
• update strict-schema docs and tests to match the runtime behavior
• make VSIX build robust on Windows by adding Python runner fallback (python3 -> py -3 -> python)

Validation

• node --test test/provider-augment-chat.test.js
• npm test
• npm run check:payload-syntax