Add Go package documentation comments to clarify the purpose and scope of:
- internal/handlers/: HTTP request/response handlers for authentication,
libraries, media items, reading, collections, dashboards, devices,
analytics, and system features
- internal/services/: Core business logic layer including media scanning,
library management, search, analytics, and conversion services
These doc comments improve code discoverability and help developers understand
the architectural separation between HTTP handling (handlers) and business
logic (services).