Fix repo compliance issues for awesome-list standards

[QDenka]

Summary

Fix several compliance and consistency issues identified during an audit against the awesome-list guidelines.

Changes

• Fix lint workflow — add fetch-depth: 0 for correct repo age checks, remove redundant push trigger (only pull_request is needed)
• Add Code of Conduct — create CODE_OF_CONDUCT.md with Contributor Covenant v2.1 and update the link in CONTRIBUTING.md to point to the local file
• Fix ordering contradiction — PR template checklist now says "bottom of the relevant section" matching CONTRIBUTING.md (was "alphabetical order")
• Fix section heading — replace & with and in "Community and Conferences" for a cleaner ToC anchor (#community-and-conferences instead of #community--conferences)

Verification

• npx awesome-lint passes cleanly after all changes