refactor(stores): resolve the store backend and its loader slot explicitly

Store loading picked the backend and the loader's process slot in one
function, which let an explicit `backend` argument collide with the
store's own config and made traces report a fixed "local-store".

This changes /stores/* behaviour for every store:

- An explicit `backend` that differs from the one named in the store's
  model config now gets its own loader slot, `<store>@<backend>`, so it
  no longer reuses (or evicts) the process of the configured backend.
  Naming the configured backend, or one of its aliases, keeps the
  store's own slot.
- When the config names a different backend than the explicit one, the
  config's `options` are not passed on, since they are meant for the
  configured backend. A config without `backend:` still passes its
  options to the explicit backend.
- Backend names are compared and reported in canonical form (aliases
  resolved, lower case) through the new model.CanonicalBackend, and
  traces record the backend that was actually used instead of always
  "local-store".

Backend loading itself uses CanonicalBackend for alias handling; type
aliases keep their existing effect.

Signed-off-by: Anush008 <mail@anush.sh>
Assisted-by: Claude Code:claude-sonnet-5-5
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

pkg/model/initializers.go

@@ -37,6 +37,14 @@ var Aliases = map[string]string{
 	"stablediffusion":        StableDiffusionGGMLBackend,
 }
 
+func CanonicalBackend(name string) string {
+	b := strings.ToLower(name)
+	if real, ok := Aliases[b]; ok {
+		return real
+	}
+	return b
+}
+
 var TypeAlias = map[string]string{
 	"sentencetransformers":   "SentenceTransformer",
 	"huggingface-embeddings": "SentenceTransformer",
@@ -337,17 +345,9 @@ func (ml *ModelLoader) backendLoader(opts ...Option) (client grpc.Backend, err e
 			"f16", opt.F16Memory)
 	}
 
-	backend := strings.ToLower(o.backendString)
-	if realBackend, exists := Aliases[backend]; exists {
-		typeAlias, exists := TypeAlias[backend]
-		if exists {
-			xlog.Debug("alias is a type alias", "alias", backend, "realBackend", realBackend, "type", typeAlias)
-			o.gRPCOptions.Type = typeAlias
-		} else {
-			xlog.Debug("alias", "alias", backend, "realBackend", realBackend)
-		}
-
-		backend = realBackend
+	backend := CanonicalBackend(o.backendString)
+	if typeAlias, ok := TypeAlias[strings.ToLower(o.backendString)]; ok {
+		o.gRPCOptions.Type = typeAlias
 	}
 
 	modelFileName := o.modelFile