feat: improve qwen code developer onboarding

[Dankosik]

Summary

• Rewrite the README around the developer quick start, Qwen Code configuration contract, security posture, and release flow.
• Improve npm/GitHub discoverability with clearer package description and keywords.
• Keep the audited Qwen Code contract anchors visible for docs contract tests.

Release pipeline

• This branch uses a releasable feat: commit: feat: improve qwen code developer onboarding.
• After this PR merges to main, Release Please should open/update the release PR with the version bump and changelog.
• After the Release Please PR merges, the npm trusted publishing workflow should publish the tagged release with provenance.

Verification

• rtk npm run ci
• rtk npm pack --dry-run --json
• rtk git diff --check