feat(model-server): wizard V2 config modèles locaux — source, options structurées & preview

Refonte UX du wizard de configuration des modèles locaux du serveur
llama.cpp intégré, alignée sur la source Hugging Face et les options backend.

- choix de source sans jargon (chemin local .gguf vs dépôt Hugging Face) ;
- champs structurés -ngl (gpu_layers), -c (context_size), --jinja, --host ;
- zone d'arguments libres avec alerte sur les flags réservés ;
- preview de la commande via le backend (previewModelServerCommand, debounced) ;
- gateway/ports et mock adaptés au contrat V2.

QA : Vitest 22 verts, tsc/build OK.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/ports/index.ts

@@ -26,6 +26,7 @@ import type {
   LayoutOperation,
   LayoutTree,
   LocalModelServerConfig,
+  ModelServerCommandPreview,
   Memory,
   MemoryIndexEntry,
   MemoryLink,
@@ -649,8 +650,9 @@ export interface CloneOpenCodeProfileFromSeedInput {
 /**
  * Local model servers (F35). CRUD over the global registry of declared
  * `llama.cpp` servers an OpenCode profile can bind to via
- * `OpenCodeConfig.localModelServerId`. Mirrors the three backend commands
- * (`list_model_servers`, `save_model_server`, `delete_model_server`).
+ * `OpenCodeConfig.localModelServerId`. Mirrors the backend commands
+ * (`list_model_servers`, `save_model_server`, `delete_model_server`,
+ * `preview_model_server_command`).
  */
 export interface ModelServerGateway {
   /** Lists the declared local model servers. */
@@ -665,6 +667,15 @@ export interface ModelServerGateway {
    * `model_server_in_use` when a profile still references it.
    */
   deleteModelServer(serverId: string): Promise<void>;
+  /**
+   * Builds the `llama-server` command line the backend would launch for the
+   * draft config, without persisting it. The backend is the sole authority on
+   * the argv (never reconstruct it client-side). Rejects when the config is
+   * invalid (e.g. `modelSource` missing).
+   */
+  previewModelServerCommand(
+    config: LocalModelServerConfig,
+  ): Promise<ModelServerCommandPreview>;
 }
 
 /** Input for {@link EmbedderGateway.saveEmbedderProfile}. */