feat: update docs for token efficient usage

backend/src/features/CLAUDE.md

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+# backend/src/features/
+
+Feature capsule directory. Each feature is 100% self-contained with api/, domain/, data/, migrations/, tests/.
+
+## Subdirectories
+
+| Directory | What | When to read |
+| --------- | ---- | ------------ |
+| `admin/` | Admin role management, catalog CRUD | Admin functionality, user oversight |
+| `auth/` | Authentication endpoints | Login, logout, session management |
+| `backup/` | Database backup and restore | Backup jobs, data export/import |
+| `documents/` | Document storage and management | File uploads, document handling |
+| `fuel-logs/` | Fuel consumption tracking | Fuel log CRUD, statistics |
+| `maintenance/` | Maintenance record management | Service records, reminders |
+| `notifications/` | Email and push notifications | Alert system, email templates |
+| `onboarding/` | User onboarding flow | First-time user setup |
+| `platform/` | Vehicle data and VIN decoding | Make/model lookup, VIN validation |
+| `stations/` | Gas station search and favorites | Google Maps integration, station data |
+| `user-export/` | User data export | GDPR compliance, data portability |
+| `user-preferences/` | User preference management | User settings API |
+| `user-profile/` | User profile management | Profile CRUD, avatar handling |
+| `vehicles/` | Vehicle management | Vehicle CRUD, fleet operations |