Saving storage settings now activates the selected driver immediately
instead of staging it until migration. When the driver changes, existing
upload rows are repointed to the new storage_driver so /f/{id} reads use
the correct backend. ForDriver can also open non-active drivers from the
saved multi-backend config.
Introduce internal/repository for data access and cache-backed system
config reads. Move business logic into logics.go across admin push,
user, template, cache, system_config, and upload/handler packages.
Remove Gin from internal/util by relocating request-scoped helpers to
oauth/gin_context.go. Propagate request context for config lookups in
user flows. Slim model entities and delete model-level DB/cache helpers.
Wire handlers to logics/repository so targeted packages no longer call
db.DB directly. Update admin router tests to use ErrorHandlerMiddleware.
ryan