feat: update docs for token efficient usage

frontend/src/CLAUDE.md

@@ -0,0 +1,20 @@
+# frontend/src/
+
+## Files
+
+| File | What | When to read |
+| ---- | ---- | ------------ |
+| `App.tsx` | Root component with routing | Route configuration, layout structure |
+| `main.tsx` | Application entry point | Provider setup, initialization |
+| `index.css` | Global styles | Base styling, CSS imports |
+| `vite-env.d.ts` | Vite type definitions | TypeScript environment types |
+
+## Subdirectories
+
+| Directory | What | When to read |
+| --------- | ---- | ------------ |
+| `features/` | Feature modules (pages, components, hooks) | Feature development |
+| `core/` | Shared infrastructure (auth, api, store) | Cross-cutting concerns |
+| `components/` | Root-level shared components | App-wide UI components |
+| `pages/` | Page-level components | Page structure, routing targets |
+| `shared-minimal/` | Minimal shared UI (skeletons, theme) | Reusable UI primitives |