refactor(server): final writeErr migration + ErrNotFound aliases (T3c)

internal/lidarr/errors.go

@@ -1,6 +1,10 @@
 package lidarr
 
-import "errors"
+import (
+	"errors"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
+)
 
 // Sentinel errors. Callers branch on these via errors.Is, not on
 // HTTP status codes — the client maps codes to errors.
@@ -15,5 +19,9 @@ var (
 	// Lidarr's monitored set. Distinguished from network/auth errors so admin
 	// handlers can surface it as `lidarr_album_lookup_failed` (502) instead
 	// of `lidarr_unreachable` (503).
-	ErrNotFound = errors.New("lidarr: not found")
+	//
+	// Aliased to apierror.ErrNotFound so handler error mapping (errors.Is
+	// against the shared sentinel) and existing per-package callsites both
+	// resolve to the same pointer.
+	ErrNotFound = apierror.ErrNotFound
 )