[codex] fix: respect Accept q weights during media negotiation

[MicroMilo]

Summary

Fixes #152.

This updates response media type negotiation in createHandler to parse Accept header q weights before selecting a supported response type. Media ranges with q=0 are now skipped, missing q still defaults to 1, and when more than one supported type is acceptable the handler keeps the highest-weight candidate while preserving header order for ties.

Tests

• node .yarn/releases/yarn-4.0.2.cjs test tests/handler.test.ts --run
• node .yarn/releases/yarn-4.0.2.cjs check:type
• node .yarn/releases/yarn-4.0.2.cjs check:lint
• node .yarn/releases/yarn-4.0.2.cjs check:format

I also tried npx -y node@20 .yarn/releases/yarn-4.0.2.cjs test --run; tests/use.test.ts no longer hits the local Node 25 uWebSockets.js incompatibility under Node 20, but the full suite still has existing environment-sensitive snapshot mismatches in tests/client.test.ts (Headers internal representation) and tests/audits.test.ts (html-validator adds a version field).

[linux-foundation-easycla]

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