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, 2 insertions, 2 deletions

diff --git a/internal/scanner/scanner.go b/internal/scanner/scanner.go
index d1e50ba..15a4949 100644
--- a/internal/scanner/scanner.go
+++ b/internal/scanner/scanner.go
@@ -38,12 +38,12 @@ type FSScanner struct {
 }
 
 // NewFSScanner creates a filesystem scanner with injected dependencies.
-func NewFSScanner(store repository.ScannerStore, prober probe.Prober, thumbGen thumb.Generator, clk clock.Clock, mediaRoot string) Scanner {
+func NewFSScanner(store repository.ScannerStore, prober probe.Prober, thumbGen thumb.Generator, clk clock.Clock, mediaRoot string) *FSScanner {
 	return NewFSScannerWithLogger(store, prober, thumbGen, clk, mediaRoot, slog.Default())
 }
 
 // NewFSScannerWithLogger creates a filesystem scanner with an injected logger.
-func NewFSScannerWithLogger(store repository.ScannerStore, prober probe.Prober, thumbGen thumb.Generator, clk clock.Clock, mediaRoot string, logger *slog.Logger) Scanner {
+func NewFSScannerWithLogger(store repository.ScannerStore, prober probe.Prober, thumbGen thumb.Generator, clk clock.Clock, mediaRoot string, logger *slog.Logger) *FSScanner {
 	if logger == nil {
 		logger = slog.Default()
 	}