feat(backend,application,frontend,domain,web-server,app-tauri): bouton Redémarrer l'agent dans la barre supérieure des cellules — #317 (QA verte)

La cellule expose un bouton Redémarrer l'agent valable pour les trois
modes de présentation (headless, TUI native, CLI custom), sans jamais
prendre la présentation pour vérité runtime.

- Application: use case RestartCellAgentRuntime validant le binding
  exact cellule/runtime via les snapshots live (RestartRuntimeNotFound,
  ConflictAgentVisibleElsewhere, AgentNotBoundToCell) puis déléguant au
  scheduler self-restart existant (schedule_cell); CellAgentPresentation
  purement informationnelle.
- Backend/app-tauri/web-server: commande restart_cell_agent sur contrat
  DTO identique Tauri/HTTP, stop borné par timeout typé
  (RestartStopTimeout), relance préservant routage TUI natif, géométrie
  de cellule (node/rows/cols) et conversation; évenements domaine
  enrichis.
- Frontend: bouton dans la barre de cellule avec confirmation,
  overlay d'état Redémarrage…/échec (libellés par code d'erreur, Fermer/
  Réessayer), gardes d'identité de cellule et de restarts externes,
  gateway/mock/http adapters et ports alignés.
- Tests: dto_agents, workstate_actions, contrats web-server,
  LayoutGrid.cellControlsLayering, adapters agent/mock/http.

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

frontend/src/adapters/mock/index.ts

@@ -164,6 +164,8 @@ import type {
   PluginWorkspaceWriteTextInput,
   ReattachResult,
   ReattachAgentChatResult,
+  RestartCellAgentRuntimeInput,
+  RestartCellAgentRuntimeScheduled,
   RemoteGateway,
   ReviewPluginPackageInput,
   SetProjectPluginEnabledInput,
@@ -406,6 +408,7 @@ export class MockAgentGateway implements AgentGateway {
   private contexts = new Map<string, string>();
   /** Monotonic session counter for deterministic session ids in tests. */
   private sessionSeq = 0;
+  private restartSeq = 0;
   /** Live agent PTY sessions, kept across detach so reattach can find them. */
   private sessions = new Map<string, MockPtySession>();
   /**
@@ -568,6 +571,37 @@ export class MockAgentGateway implements AgentGateway {
     return stopped;
   }
 
+  async restartCellAgentRuntime(
+    input: RestartCellAgentRuntimeInput,
+  ): Promise<RestartCellAgentRuntimeScheduled> {
+    const known = this.getAgents(input.projectId).some(
+      (agent) => agent.id === input.agentId,
+    );
+    const sessionId = this.liveSessionByAgent.get(input.agentId);
+    if (!known || !sessionId) {
+      throw {
+        code: "RUNTIME_NOT_FOUND",
+        message: `agent ${input.agentId} has no live runtime`,
+      } as GatewayError;
+    }
+    if (this.liveByAgent.get(input.agentId) !== input.nodeId) {
+      throw {
+        code: "AGENT_NOT_BOUND_TO_CELL",
+        message: `agent ${input.agentId} is not bound to cell ${input.nodeId}`,
+      } as GatewayError;
+    }
+    this.restartSeq += 1;
+    return {
+      restartId: `mock-restart-${this.restartSeq}`,
+      status: "scheduled",
+      agentId: input.agentId,
+      nodeId: input.nodeId,
+      kind: this.liveKindByAgent.get(input.agentId) ?? "pty",
+      presentation: input.presentation,
+      layoutId: input.layoutId ?? null,
+    };
+  }
+
   async createAgent(projectId: string, input: CreateAgentInput): Promise<Agent> {
     const list = this.getAgents(projectId);
     const slug = slugify(input.name) || "agent";