docs(repo): define agent skills and frontend cookbook workflow

AGENTS.md

@@ -6,6 +6,17 @@ This file provides guidance to AI coding agents when working with code in this r
 
 This is a monorepo with **backend** and **frontend** directories.
 
+## Agent Skills
+
+Use repository skills when applicable:
+
+- `svelte-code-writer`: required for creating, editing, or analyzing `.svelte`, `.svelte.ts`, and `.svelte.js` files.
+- `frontend-design`: use for frontend UI, page, and component design work.
+- `conventional-commit`: use when drafting commit messages that follow Conventional Commits.
+- `gemini-api-dev`: use when implementing Gemini API integrations, multimodal flows, function calling, or model selection details.
+
+When editing frontend code, always follow `docs/frontend-design-cookbook.md` and update it in the same change whenever you introduce or modify reusable UI patterns, visual rules, or shared styling conventions.
+
 ## Commit Guidelines
 
 This repository uses Conventional Commits (e.g., `feat(api): ...`, `fix(frontend): ...`, `test(models): ...`). Always format commit messages accordingly and ensure you include the correct scope to indicate which part of the monorepo is affected.