feat: add frontend development guidelines and structure documentation

- Introduced API guidelines for interface contracts and request handling.
- Added design tokens usage guidelines for consistent styling across the project.
- Established DTO guidelines for defining request parameters and response data types.
- Created frontend structure guidelines to clarify directory organization and code placement rules.
- Compiled a comprehensive frontend development guideline document covering various aspects of the development process.
- Implemented quality guidelines to ensure code maintainability and adherence to best practices.

AI Coding/assets/index.md

@@ -0,0 +1,13 @@
+# Assets
+
+索引由成熟经验产生的可执行资产：
+
+- global-agents
+- repo-agents
+- skills
+- hooks
+- scripts
+- evals
+- templates
+
+资产的实际 source of truth 可以在对应项目或 `~/.agents/skills` 中；这里记录来源 learning、目标路径和验证方式。