refactor(service,scanner): return concrete types from constructors

Apply the Go best-practice convention 'accept interfaces, return concrete
types' across the service and scanner packages:

- NewBrowseService           -> *browseService
- NewWriteService            -> *writeService
- NewMediaStreamer           -> *mediaStreamer
- NewFSScanner               -> *FSScanner
- NewFSScannerWithLogger     -> *FSScanner
- NewPodcastBrowseService    -> *podcastBrowseService
- NewTagService              -> *tagService
- NewShareService            -> *shareService
- NewProgressService         -> *progressService
- NewAdminService            -> *adminService
- NewAdminServiceWithLogger  -> *adminService
- NewAuthService             -> *authService
- NewNoteService             -> *noteService
- NewFavService              -> *favService
- NewMediaService            -> *mediaService
- NewMediaServiceWithPodcastBrowser -> *mediaService

Callers continue to work unchanged because Go allows assigning a concrete
type to an interface variable. All tests pass with -race -cover.

1 files changed, 1 insertions, 1 deletions

diff --git a/internal/service/progress.go b/internal/service/progress.go
index 376ebb7..ef248cf 100644
--- a/internal/service/progress.go
+++ b/internal/service/progress.go
@@ -17,7 +17,7 @@ type progressService struct {
 }
 
 // NewProgressService creates a concrete ProgressService.
-func NewProgressService(store repository.ProgressServiceStore, clk clock.Clock) ProgressService {
+func NewProgressService(store repository.ProgressServiceStore, clk clock.Clock) *progressService {
 	return &progressService{
 		store: store,
 		clock: clk,