skill: create `add-new-model` and `code-review` (#26042)

skill: create `add-new-model` and `code-review` (#26042)

* skill: add new model

* add common pitfalls

* add code review skill

* nits

* add codeowners

* add security review section

* mention about skills in agents.md

* add design review

* exclude ggml-gh-bot

* Apply suggestions from code review

Co-authored-by: Piotr Wilkin (ilintar) <redacted>
Co-authored-by: Xuan-Son Nguyen <redacted>
* conversion-time weight modification

* nits

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Co-authored-by: Piotr Wilkin (ilintar) <redacted>