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.

.obsidian/appearance.json

@@ -0,0 +1 @@
+{}